I hear all kinds of stuff about folks who run "evil" campaigns (of Dungeons & Dragons) and really struggle with why their game falls apart. I think the secret is that they're trying to run Evil with a capial "E" when they really need to lower-case it. If all of your characters aspire to be Sauron or Emperor Palpatine, well, yeah, it's going to be difficult.
That said, I've never had a problem with characters who were unwilling to actually play the game just because they wrote "evil" somewhere on their character sheet. In fact, it is my intention to completely minimize if not excise alignment from the game. I never have an alignment requirement, and I rarely even care if the PCs pick an alignment or not. As a result, I've had no shortage of really shady characters over the years.
Some notable evilness from past (and current) campaigns: Fulcrum, the evil gnome sorcerer. At one point, in the city of Greyhawk, when a doppleganger attempted to frame us, he just let loose with a fireball on a crowd of peasants in a tavern. Burned most of them to a crisp. We chased the doppleganger into the street and killed him, then Fulcrum framed him for casting the fireball. Since nobody was really alive to contradict him, and all the goody-goody characters weren't witnesses exactly, he got away with it. Although to mollify the cleric of Heironeous, he did raise some money for the widows and orphans. Although he gambled to win it, and ended up losing it all before he actually gave it to them. Nice PR, Fulcrum.
Eladkot was another gnarly little sorcerer. Human. After fighting off a glimmer imp, a peculiar fey that steals the eyes of innocent victims, Eladkot realized that if the eyes were popped back into the victim's head and a simple remove blindness spell cast on them, they'd not only get their vision back, but have some added benefits as well for the trouble of having your eyes in a fey's sockets for a while. He "heroically" volunteered to take the young victim to a cleric to have her eyes returned to her. Needless to say, the brown-eyed Eladkot came back the next morning with green eyes. He defends his actions as saying that he let the poor girl keep his eyes, so she really doesn't have anything to complain about.
That was merely the preview of his evil, though. When they were in the demon-god worshipping pirate town of Blackport, they were recommended to a diviner to get some more information. When they found out that the diviner used anthropomancy (i.e., reading the future in the entrails of sacrificial victims. Human sacrificial victims. Well, humanoid. This is D&D after all.) most of the rest of the party said they wouldn't have anything to do with it. Eladkot, however, snuck out at night, bought the cheapest slave he could find and visited the diviner while the rest of them slept. The diviner---a possessed little girl---gave him his readings with her hands thrust into the guts of a dying old halfling.
When the rest of the players found out what had happened early the next session... wow, that was one of my favorite DM moments ever. At this point, half of them were convinced that they should head back to the diviner with more questions. And when they were attacked by a press-gang, that is actually what they ended up doing. The peculiar morality of some of the rest of them revolted against slavery, but didn't have any problems with killing honest-to-goodness prisoners.
Corey and Brian, the players of Ricardo and Lash respectively, have commented on the evil with a little "e" vibe in my "Demons in the Mist" game. Which is fun, because they're probably the more overtly evil characters, if you were to try and put a label on it. Ricardo is charming and attractive... until you get to know him a bit. Corey's really nailed it on the head when he made his rake an angry and selfish individual that cares little for his conquests, and quite probably is the way he is as a coping mechanism for being psychotically damaged in some way. Lash has glimmerings of caring about people around him... from time to time... but mostly is content with pursuing, by hook or crook, his own dreams of wealth and leisure regardless of the cost to anyone else. This has been the source of a great deal of comedy, as the two of them "compliment" each other in a lot of ways, by which I mean that their combined weaknesses and tragic flaws ensure that they are pretty much in a state of constant trouble. And, currently, they have the tools to prevent (or cause) the End of the World™ in their hands, but they're not sure they care to do anything about it, because they don't see what's in it for them, and they have just enough hubris to think that they don't need to because it'll never impact them personally.