Celebrity Resemblance: He has a passing resemblence to a bearded John Simm, to the point where the Ashens Action Figure was a modified version of the Master from the new series of Doctor Who (played by Simm)
Many have noted his resemblance to Simon Pegg, especially when paired with Guru Larry, who--also noted by many--acts as Ashen's NickFrost.
The Simon Pegg resemblance was visually lampshaded in "An Excellent Newsflash".
Ear Worm: His opening theme. Liquid Filth also counts.
And the song he improvised on the iPhone's LaDiDa app which he titled Aqful (spelt instead of Awful because of the iPhone's awkward keyboard).
Ensemble Darkhorse: The Godmonster of Indian Flats seems to be very popular, as he's had to address why there haven't been more of him. It's because he was scarcely in one movie. He hopes to grow a guinea pig into a new one.
Quincy, the Caterpillar who sings obscure Beatles songs, is also pretty popular.
And there's the Excellent Darkhorse himself, Chef Excellence.
The degree to which he's become memetic becomes very clear in his Not 100th Video Contest showcases.
Hilarious in Hindsight: A Running Gag which appears when he mentions StreetOverlord is saying that, "Two men pull their arms and legs off and throw them at each other". Then Mortal Kombat 9 came out, and one of the challenges in the challenge towers has you doing exactly that.
Less Disturbing in Context: "Oh, god! It's spraying everywhere! The doctor said I wouldn't have that problem any more!" He's referring to a tube of CD cleaning fluid.
The microwavable pizza snack gets hyped up as this as well. As Stuart himself says, "NOT RECOMMENDED".
He proclaims the German creme egg-lookalikes to be the most disgusting Poundland food yet, and then whilst wondering what was going on (as he'd expected them to at least be OK because even they couldn't screw up something that simple), he notices a maggot lying on one of them. It turns out to be a fake planted there by a friend, but still.