Man, where to start?
There's the guy who wasn't really all that creepy most of the time, except years later when everyone got called to testify in court because the cops finally had enough evidence to prove that he had bashed his ex-wife's head in with a brick and then laid her across the train tracks because he wanted to see his kid.
Then the guy who burst into our Saturday night game with an arsenal of firearms, all cranked up on whatever. I'd never met him before, so everyone had to speak fairly quickly to keep him from pushing a pistol at me. After he took some more pills he pulled out a character sheet and played the game as if he were a regular member of the party...with a pile of guns underneath his pillows on the floor.
One of my friends killed himself with a shotgun early one Saturday morning. They had barely taken away the body when apparently one of the other players showed up and said, "I just heard, can I have X's Magic Cards?" and walked in and tried to take them from the grieving widow.
I've had players go out for snacks during a break and end up in prison, players literally knocking down walls of the house we were playing in, thieves, creepy molester type guys, pauses for drug deals, pauses for sex, sex at the game table, general inappropriateness, fistfights, knives drawn, unexpected revelations about sexual orientation and disturbing crushes , and unwanted sexual advances in general. I've even had a fire started by a disgruntled player kicked out for this crap.
I think only the potty-pants guy over at RPG.net really significantly overshadows my own experiences with creepy and disturbing players, but at least I'm confident that anyone doing that around any of my players would probably face a lot more significant peril than social rejection. Guns Guy would probably make him eat his own teeth, for instance.
Just to be clear though, most of these 'creepy' people weren't really bad people (except the murderer and magic cards guy). They were just screwed up young people like myself at the time that I and my friends were around already because of work or whatever and we just were really good at getting EVERYONE to game with us. And when everyone works in 'shady professions' and bars for the most part, well I guess it's probably different than when your players are all lawyers and firemen.