I love playing evil - or at least highly questionable - characters, and have done so in many RPs and many different settings. Personally, I find it more enticing than playing a goody-two-shoes; even when my characters are 'good' (by the alignment that I don't even use), they're usually the sort of stern, honor-bound, or Knight Templar good, not just 'good' good.
For, mind me, playing characters that aren't all rainbows and ponies is extremely interesting and challenging. At least for me. It requires you to think about their motivations, to put up with the disapproval from the public, to think about the moral doubts they have, to show what they even think about the 'good' characters that stand against them... And to see them either get more evil, or reform. The journey of an evil character is often more than interesting to explore - are they evil for revenge, because they were hurt, because they're power-hungry, because they're bored? Are they doing it because they know no else? Are they truly evil, even?
My first evil character was Aldanith. He didn't start off as really evil, just crude and rough; but as the story went on, he found out that he likes to be bad, that the world is evil, people are pigs and bastards, and he likes ripping them off and slitting their throats. Because the world never had anything good for him, he didn't understand the concept of love, friendship, or caring for someone; that ultimately became his doom, since he was greedy to the point of using even his own subordinates and a woman he pretended to love. When he abandoned her, unbeknownst of the fact that she would have given him a child, she begun to hate him. And his band of outlaws also stabbed him in the back and left him for dead, to be discovered by her (and have his arm sliced off). But did he think about being a bad person and reform? No, because hate only results in more hate, violence spawns violence; he got just more violent, at one point even possessed by shadow demons (officially his darkest point as of now) where he ripped people's skulls out for the fun of it. Sick guy, really. After he exorcised them, a little bit of a reform happened, but nothing radical - Aldanith still likes to kill people in brutal ways, and he's still not figured out that you can actually feel positive emotions towards a person. Currently, he's on his way to figuring it, but whether that will be successful is... Questionable at the very best. In the end, he just wants to kill his mad ex.
Lucien is a curious sort; he's not evil by himself. He's just terribly self-centered and cares so little about other people that he practically abuses them to climb the ladder of political power. He has little 'real' morals, although he has a perfect pretended etiquette; his primary motivation is to get power, as he is incredibly power-hungry. He doesn't want to live the forsaken life of a noble's bastard son that is just frowned upon and thus he does his very best to be classy, powerful, successful and all; he likes beautiful women, lavish parties, and expensive clothes, which are all just status proofs in themselves. He wants to be recognized and he wants everyone to serve him, he wants to be in control, because he simply loathes the idea of something being on a position higher than himself and being able to give him commands.
"Fangs", aka Grian, is more of an anarchistic rebel that disregards any sort of authority and the value of human life and other people's emotions rather than being evil. He doesn't want bad stuff to happen to other people - he simply doesn't care about what happens to them as long as he's enjoying himself and having fun, even if that means smacking someone into utter oblivion or beating a man into a bloody pulp; does it count as enjoyable to him? Yes. So, it's not wrong. He just has no sympathy and no care for laws and orders, even the social ones. He was raised in a strict household which he hated, and now he does his best to defy it; however, he's also scared. Scared of dying soon, and he knows he IS going to die soon, what is why he wants to enjoy himself as much as possible before he's gonna be out there and on his way to the fiery pits of hell or whatever. He wants to have fun really badly, he wants to prove that he's the best at what he does - treasure stealing and tomb robbing, like some sort of a mad kickass Indiana Jones with blue hair, nunchucks and no moral code - and that he's going to go out in style. Practically trying to pack the what, 25 years he'd normally have left into a mere 10 or such.