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Later as he's shot by Frieza, Goku tells him that if all this wouldn't have happened to him, he would be evil, and Vegeta replies "Ohh, no, I'd still be evil. If the situation were reversed, this conversation would never have happened. You'd be dead, and I'd be laughing."
The Circle of Cold Flames, from the Global Guardians PBEM Universe, is an order of mystics and sorcerers dedicated to overthrowing Heaven and instituting a reign of evil over the earth (and putting themselves in control over it all in the end). They even describe themselves and their plans as evil when talking to one another.
The Evil Gamer, evil twin brother of The Irate Gamer, he constantly uses the word "evil", lives in the "Castle Of Evil", and wanted to do an "evil Aflac Duck" for the Aflac audition sketch.
Vendetta. In the web cartoon, Vendetta's main reason to destroy Charlotte seems to be because she thinks Vendetta and the fiends are nice and her friends, although in the TV series, this boils down to "Charlotte is annoying". Same with Mrs. Minty, who is unaware(?) of Vendetta's evilness and treats her like another misbehaving student, which doesn't end well.
Mr. 'Freaking Stinking Cheating' Doom of the Mario Party TV group doesn't particularly mind being seen as the token evil teammate, and uses this as an excuse whenever the others get salty.
Ganondorf, from the Machinima series Melee's End, seems to only act as an antagonist because he was designed as a bad guy.
In Nocte Yin, about a third of the population has Villain in the job description and most of them fall under this category.
SCP-353 of the SCP Foundation is a Plague Master who refers to herself only as "Vector", gathers new types of infectious agents "because I can", and is considered by the staff to have "X-men villain fantasies".
Bennett The Sage outdoes both of them, though—he's traumatized Ask That Guy mentally and physically, and Insano has been shown to have soft spots. Hell, Sage has even claimed to be Satan on multiple occasions (though whether he actually is or not depends on what video you're watching.)
In Unforgotten Realms, the Evil Overlord Timmy the Evil spends his evil time discussing his evil plans for the destruction of the not-so-evil heroes with the evil Professor Walrus. All of his evil plans so far include using evil crystals with a variety of evil powers. Evil.