Bob the Angry Flower once had a violent confrontation with a man who only gave his name as the Evil Business Guy Made of Butter. Well, allegedly had a violent confrontation with an alleged Evil Business Guy made of pure creamy butter.
Seren of Karin-dou 4koma has a demon lord license. It expired more than twenty years ago after she forgot to renew it, but she's thinking about reapplying now that she has free time. It's actually just a LARP thing, though; the true demon lord is locked in Seren's closet.
Helen, Mell, and, later, Dave in Narbonic. Helen is, in fact, a Shirt Wearing Villain — her habitual outfit includes an old T-shirt which reads "evil", with a heart dotting the i.
A certain story arc in Nodwick involved him being captured by the Brotherhood of Evil Henchmen in an attempt to get him to do a Face-Heel Turn and devote his henching skills to their benefit. The guild master gleefully explained at one point that they only worked for villains.
Xykon from The Order of the Stick (as seen in the trope image) prides himself on his evilness. This pride is justified.
As do their masters, the Inter-Fiend Cooperation Commission, though, considering they're fiends (and therefore literal incarnations of evil), this trope rather goes with the territory.
Redcloak is an interesting example: he admits he and his god are evil by Dungeons and Dragons alignments, but he still thinks his actions are justified. He seems to think of alignments as being more like team names than actual moral judgments (which they were initially intended to be, in fact. It gets rather weird from there).
Elan's long-lost father turned up and explained why he chose to become an evil tyrant: every story calls for one, so he will be the villain and "live like a god for three decades" until some heroes come along to vanquish him. He'll still be immortalized in bardic lore and he'll get to be emperor for a while, so, in his opinion, eventual Karmic Death is worth the payoff. He does, however, reject the alignment system as "outdated and meaningless" so it's possible that he's a subversion.
In Yet Another Fantasy Gamer Comic, all of the monsters of the mountain identify themselves as evil, though only the Drow (and King Louie the Liche) act like it. The only real difference between the rest of the monsters and the "good" humans and elves are a tendency to eat other sentient beings and a casual approach to mortal violence. Can be meta-Lampshade Hanging on the initial idea of alignments as sides in the war: you don't really have to pass an Evil Test to side with your family, do you?
Black Mage Evilwizardington in 8-Bit Theater, if his last name didn't give it away already.
Hell, he even tried joining the bad guys after gleefully wasting all his fire spells on BATS and leaving the Light Warriors to die inside a block of solid ice:
Drizzl: What do you think you're doing? Black Mage: I'd say I was joining the winning side, but that would imply that there was some point where I wasn't part of team evil.