I agree with Frosty. I've seen plenty of good RPers pull off evil characters without being disruptive of the game or getting in the way of anyone else's enjoyment. If someone just wants to run around, eat babies and set towns on fire, they're a ****ty player. On the other hand, you have those classic lawful stupid paladin characters that are played as disruptively as possible: gloryhounding, bossing other players around, attacking NPCs at the drop of a hat and just generally being an incredible ass. Ironically, I ban paladins for the reasons people ban evil characters, but someone may be able to sell me on it with a good concept.
Either way, I like to get a good enough feel for your character at creation that we can figure out what alignment works best for that concept. Alignment is always explained as a guideline for RP, but that's complete BS, it's not a real motivation that an actor could use. Instead, I look at it as a challenge for good RPers that already have viable motivations for their characters.
Anyhow, here's some advice on playing or running evil characters:
Make sure you define lines you don't cross, both players and NPCs - I don't allow any rape or harming of children. I don't care if it's some demonspawn child taking swipes at your throat, you're not killing it or you're out of my game. If you're uncomfortable with anything evil PCs might do, you might just be uncomfortable with it being in the game at all, so call it out and make sure your NPCs aren't doing it either.
Your character may not actually be evil - I mentioned before that I like to sit down during chargen, hear a PCs motivations and then figure out an alignment from that. Maybe you just want to play a guy who's all about carrying out some evil act like murdering some particular person for petty reasons, but otherwise they're pretty decent. There's no reason to saddle him with an evil alignment and all the baggage that comes with it.
Not all evil characters eat babies - Everyone has lines they don't cross, even evil guys. Evil guys can have close friends too, like y'know, maybe the group of adventurers they clown around with all the time. There's always a chance an evil character can redeem themselves too. I've seen plenty of evil PCs sacrifice themselves for the good of the group, pull a Darth Vader, but in 20+ years of gaming I've -never- seen a Paladin sacrifice himself. Seriously, people should be banning Pallys instead of evil.
If a PC betrays the party, they're done - Everyone dreads when that evil guy will betray the group, but it can only happen once and that PC is effectively dead after that. That's pretty serious business and you can be sure that -if- that moment ever comes you'll be able to get some really good drama out of it. So, why not?
Adventure should be priority #1 - This really fixes a whole slew of problematic characters. Imagine playing Bilbo and deciding to stay at home instead of leaving with the party. Or imagine Reed Richards decides to sit at home and do science all day instead of fighting bad guys because he's a scientist. That's really a lot worse than the character who wants to loot dungeons because he's greedy. If an evil character's main priority is adventure, how likely is he to mess with the other PCs or betray the party if that ends his adventure? Like Bilbo, you can even play a character who hates adventure as long as he goes along with it anyway.