England: In canon, he's a snarky Tsundere who has had his days of pillaging and plundering as a pirate and frequently gets into fights with America or France, but is more bark than bite and clearly has a softer side (he's not called a Tsundere for nothing, after all), is more Vitriolic Best Buds than outright enemies with America and France, and suffered (and probably still is suffering) from heartbreak due to the one he cared for the most leaving him. In fanworks, one side of his Tsundere personality is all too often exaggerated at the expense of the other - and when said exaggerated side is the 'tsun', he becomes a Manipulative Bastard who only cares about himself, his empire, and/or forciblypossessing his object of desire. Becomes especially bad if Russia is made into the Draco in Leather Pants opposite of him, or America is woobiefied into an innocent and helpless victim.
America: In canon, he's a boisterous and denseditz, but ultimately a good-heartedLove Freak who can be a jerk to Canada or England but not all the time. When rabid Canada fans or militant England/someone-other-than-him shippers get a hold of him, however, he either becomes a Complete Monster of a Jerk Jock who abuses and victimizes poor, neglected, widdle Mattie-kins or a total moron and asshole who can't accomplish anything with England other than breaking his heart again, or throws away all the proofs of affection that they've given each other in order to completely conquer the world and oppress it (double if they make England a Purity SueLove Martyr as well).
Some fans also flanderize the complex issues surrounding the US atomic bombings and occupation of Japan at the end of WWII into "America is a Bespectacled Bastard Boyfriend or psychotic Yandere who abuses/rapes a weepy, horribly traumatized Japan". How this sadist!America and traumatized!Japan could ever have become the good friends they're canonly shown to be before and after WWII (not to mention the good allies they are in real life) is a mystery.
Or his Westernanti-fans from taking any of his traits, positive or negative, and blowing them way out of proportion to "prove" what a "horrible" character he is; his Japanese Politeness will be taken as proof that he's an Extreme Doormat, his occasional passive-aggressiveness as proof that he's a manipulativesociopath, his slight Ship Tease with other characters as proof that he's a Mary Sue harem lead who has half of the cast fawning over him (not to mention how attacks on his character coincidentallypeaked when episodes of him with Greece and Turkey aired...), etc.
Really, the fact that he gets along well with Greece, should be enough proof all on its own that he's not some sociopathic bastard who cares only about himself. It also can't be a coincidence that almost all fanworks that invoke this trope with him the hardest never even mention Greece in passing relation to him and that the few Dark Fics that do mention Greece have Japan ultimately be sympathetic or at least show some redeeming traits.
Morality aside, can you really picture a man who thinks that being hugged ruined him for marriage raping anyone?
China: For some other fanworks, you can swap Japan and China's names in the above "Bastard Boyfriend / Yandere" sentence and have it be just as accurate a description, but with even less justification. Yes, real-life China isn't exactly a bastion of human rights, but real-life nation =/= Hetalia nation-tan, especially when said nation-tan is a quirky and sympathetic panda lover. A nagging, old-fashioned, clingy China who treats his younger siblings like little children and except for Korea drives them away from him when he tries to help them or unintentionally embarrasses them with his old man behavior is canon; a Yandere or Complete Monster China who abuses/beats up/rapes Korea, Vietnam, Taiwan and Hong Kong into submission during either Imperial or Red times, used to abuse Japan in every possible way (and preferentlysexual ones) when he was a kid and/or heartlessly approves of the massacres of either his own or other nations's citizens by any of his governments is not.
Romano/South Italy: Apparently, the fact that he's got a Hair-Trigger Temper and feels like The Unfavorite in comparison to Veneziano/North Italy makes him a Complete Monster of a Bastard Boyfriend towards Spain who needs to be "saved" by France (Him showing genuine concern for Spain in canon when the latter fell ill? Surely you jest!). His harshness towards his younger brother is also occasionally ramped in fandom, going as far as to have him portrayed raping Veneziano to "keep him in check" or out of jealousy of his talents.
This is so bad sometimes that there recently was wank about it on the Hetalia kinkmeme. A well-known Romano basher who thinks "he is abusive in canon towards Spain" has been accused more than once of spamming it with either Romano-bashing comments or requests in which she asks for fics where Romano is killed or beaten up for abusing Spain. Much lulz and facepalms were had.
Brought up again recently in the comments to a fill that includes "Romano as a closeted homophobe". The author was handling the very "dangerous" prompt tastefully, and yet when she reached the point in which Romano "exploded", many fangirls started demanding for him to be punished/beaten/killed/etc., creepily equalling Romano's fic behavior with real life gay bashing, saying that Romano is an homophobe in Hetalia canon, etc. And whoever tried to break in and didn't kiss these overprojecting fangirls's butts was accused of being an homophobe and hating gays in Real Life. Sigh, seeing it gone was a relief.
Unfortunately, the Romano bashing has appeared again on the kink meme in the form of anons who claim that it's illogical for Spain to care about Romano because Romano acts so mean and horrible to him or that he cares about Romano only because he's a saintly Love Martyr and anyone less than a saint would have seen Romano for the unworthy bastard he is. In either case, they demonized Romano's Tsundere behavior as proof that he's utterly undeserving of Spain's time and attention and dismissed the signs of care and affection he's shown for Spain in canon as unimportant because he wasn't direct or clear enough with them (apparently, saying "Wa...wait for me! I'll do something about this, but I'm not promising anything!" isn't direct/clear enough) while making excuses for Spain's own faults and the times when he wasn't really helpful with Romano's feelings of inferiority or insecurity. Cue eyerolling by many other anons who pointed out that all these claims were essentially just attempts to prove that Romano is an asshole who hurts sweet innocent wonderful Spain who is NEVER EVER responsible for anything he does.
Becomes especially ridiculous when you consider that the only canon "evidence" these fans can dredge up for Romano being physically abusive towards Spain is that he peed on Spain's house (which was entirely Played for Laughs)... and that's it. Romano's often sarcastic and short-tempered with Spain but the only time he has been shown to use actual physical violence against him was a head butt when Romano was a child (because Spain was unknowingly touching his erogenous Idiot Hair) and even his Hair-Trigger Temper tends to be limited to grumbling about Spain's weird habits but still going along with them, like when he complained loudly about turtles invading his house but didn't really do anything to stop Spain from cooing over them. Heck, Norway strangles Denmark at least twice in canon and pretty much all fans agree that this is just for humor or Tsundere purposes and not an actual sign of abusive behavior; why can't Romano's comparatively mild behavior towards Spain be viewed in the same light?
Veneziano/North Italy: On the other hand, rabid Romano fangirls tend to blame Veneziano for everything that goes wrong with Romano and demonize him to make his older brother look better. It's hardly N. Italy's fault that Romano is screwed up in the self-confidence department, people, and he actually does care for Romano and shows it. And making him into a Psychopathic Manchild to woobify Germany (who of course is completely blameless of his country's WWII misdeeds) and have Prussia rescue him? Does not compute.
An example of the rabid Germancest hate against Italy is here. It's on Mediafire since image sites kill it, but it's worth the download t since it shows the butthurt and the batshit in a simply priceless way.
Turkey: Yes, he's a Boisterous Bruiser who once wanted to conquer Europe and is no friend of Hungary or Greece, but his frequent portrayal in fanworks shipping him with one of these two nations (especially the latter one) as a power/control-hungry Bastard Boyfriend who doesn't care one iota about the other's feelings aside from usinganymeanspossible to make them acknowledge his dominance over either Greece or Hungary is definitely taking it too far. Even if his personality isn't the mellowest one around, his canon protectiveness of Japan should at the very least imply a Jerk with a Heart of Gold instead of a full-blown Jerkass. And then there's his sympathetic portrayal in the Hetalia Bloodbath 2010 and his Intergenerational Friendship with Iceland.
Turkey bashing shows up in some Spain/Romano fics, stemming from a canon incident when Turkey kidnapped a young Romano, who was then rescued by Spain. Some authors push it too far, however, and make him seem genuinely evil and often with a gross obsession with Romano, often portraying him as cruel and abusive so Spain can swoop in to save Romano and show how pure and caring he is by contrast.
His treatment of Greece in numerous fics takes the cake, however. Greece abused as a kid or teen by Ottoman Empire!Turkey? Turkey raping Greece because he wants to teach him a lesson or can't control his urges anymore? All par for the course in Turkey/Greece fics, to such an extent that Greece sometimes gets caught up in this trope too, turning from a patient, laidback Kindhearted Cat Lover who gets snippy only with Turkey to an angry, violent man who's bitter towards the entire world and has no patience for anybody he thinks is stupid (which includes nations other than Turkey), just so that the fanwriter can show how his relationship with Turkey is not a Destructive Romance, even when Turkey is treating him worse than he ever did in canon, because Greece's always been like that and/or Turkey is the only one he shows his sweet side to. There is not enough room on this page to describe everything wrong about that.
(God knows what we'll have to deal with if Armenia is ever given a nation-tan . . . . . actually, strike that. Considering the official Turkish stance on that whole affair, Flanderisation would probably be quite satisfying for once.)
Prussia: More than one fan has taken his Small Name, Big Ego, Butt Monkey and Badass traits, used for comedy in the series, to all kinds of extremes. As a consequence, many fics and RP scenarios have Prussia derailed into either:
a Card-Carrying VillainComplete Monster who rapes and beats his allies and friends to keep them terrorised and under his thumbs (if he's not eating Jewish children for the lulz - yeah, that was mentioned in a really infamous RP log) and is to blame for all the German World War II atrocities while his younger brother Germany is merely "misguided by his bosses" or yet another victim of Prussia's abuse. Which, you know, completely ignores how lots of the Nazi resistance groups came from the ex-Prussian territories, among other stuff;
an absolutely brainless Jerkass whom every single European country hates to death, who stuffs himself with beer, only exists to make dumb jokes and act like a Troll without showing any good personality traits, and whose presence WILL make Hungary go automatically frying pan crazy before he can even breathe in her surroundings.
France: Yes, France is a Lovable Sex Maniac whose treatment of the nation-tans often skirts Black Comedy Rape. Yes, he can be shallow and whiny and often sucks at fighting. Yup, he can be quite the Manipulative Bastard if he wants. And yeah, he and England don't get along. However, that does NOT give fandom a pass to flanderise France into an absolute moron who only thinks with his dick, a heartless rapist who lacks any character depth and must be shot to death so he won't tie up and brutally rape the whole cast (despite how France actually denies being a rapist in canon), or a slutty Smug Snake who toys with a teen!America's feelings and insecurities (and maybe, even his body) during The American Revolution purely to spit on and laugh in the face of a Purity Stufied England who is never ever to blame for his own actions or decisions.
Spain: He is a really strange case. While Romano often gets bashed to Hell and back for being supposedly "evil and abusive" to him, he's more often than not played as a helpless and ultra-innocent woobie whose own flaws "can't be helped" and "should not be taken in account". There are some fans, however, that gleefully insist that Spain MUST actually be a Yandere or a Cute Psycho in canon, taking incidents in which he's shown not-so-nice sides that are actually Played for Laughs and blowing them WAY out of proportion.
Also, out of all the fics portraying Spain's Conquistador or Civil War days, it's highly likely that many of them will have Spain as a Yandere rapist/abuser towards his OC colonies or fellow canon nations. While the majority take the Bastard Boyfriend route, others definitely play it as this trope, and the Unfortunate Implications just can't be uglier.
And then there are the fics that portray Spain as a pervertedpedophile who regularly tries to rape the young kid Italian brothers/America/one of the old Spanish colonies/etc...
Austria: While not a super obvious case like others, there's enough evidence to put him here. The Austrian Empire has had a war-full story and the relationships with other nations (France, Hungary prior to the Austro-Hungarian Empire, Spain, etc. and specially Italy) were very conflicted, yep, but that's barely an excuse to portray him as being a Complete MonsterDomestic Abuser who regularly beats, rapes, whips, tortures and executes Hungary and North Italy. He was already a harsh Stern Teacher in canon, and yet he still did Chibitalia's work for a day so the kid would have some time alone after HRE left the manse - that's enough proof of how Austria is more complex than he looks, and even if he's a jerk in canon more than once, it's still not to Complete Monster levels.
Canada: Oh yes, believe it or not, even the sweetunassertiveNice Guy is not immune from this treatment. As mentioned above, many of Canada's rabid fangirls have a terrible habid of putting his brother America down in order to glorify him into a Sympathetic Stu. This phenomena has reached a point where it's actually costing Canada popularity points with annoyed circles in the Hetalia fandom. In particular, a good number of America fangirls who are sick of seeing America colored up as a Jerk Jock to make Canada look like a saint have issued their own retaliation. Usually, they'll exaggerate Canada's Beware the Nice Ones moments (such as that one time when he seriously chewed America out with a three hour long "The Reason You Suck" Speech) and turn him into a full fledged emotionally and verbally abusive Bitch in Sheep's Clothing, or in some cases outright Ax Crazy (mostly with a hockey stick, but at least one incident involved a chainsaw). While Canada does indeed resent his brother at times, he is shown to still care for him to some extent and their relationship is more or less normal between brothers (even if it is a little vitriolic, it's mostly played for laughs anyway).
Seychelles: Overlapping with Die for Our Ship like whoa. She's a Hot-BloodedPlucky Girl who has some Ship Tease and UST with both France and England in Gakuen Hetalia: obviously that makes her a total slutty whore who has no worth or depth as a character, is an offense to women everywhere, and must be horribly tortured and killed off.
Denmark: If there's a member of the Nordic Group that is likely to be portrayed as a total asshole in the fandom, it's Denmark. Sure, he can be pushy and Hot-Blooded and Norway sometimes hits him to keep him in line, but that doesn't mean that he raped and beated the Nordics into submission and that's why they don't seem to take him seriously. He could've perfectly treated Belarus badly in Hetaween, but he cheerfully accepted to compete with her cosplay group — shouldn't that be a sign that he isn't evil or a Jerkass?
Everyone gets this by default in the popular Porn Without Plot setup in which defeating another nation in battle requires the victor to rape them. Apart from the many, many Squick and Fridge Horror problems with this, if this was true], Austria would have noticed Italy's anatomy much sooner. Not to mention it's very hard to sympathise with a victim when you know that the logic behind the setup would have required them to have done the exact same thing themselves; doesn't by any means make it okay, but it does mess with the impact somewhat.