The above examples are pretty extreme, and in the first example, pretty darned rude. At the very least, I probably would have told the person to leave the Con and I would have refunded him out of my own pocket so the charity didn't suffer. Wanting to play an 'evil' character is no excuse. We've had plenty of campaigns where plays took evil characters and played them extremely well and it wasn't disruptive to the players. Maybe it caused issues for the PC's in game, but everyone had fun with it and adjusted their actions, but the story was still cohesive.
For me, the 'difficult' player is the Meta-gamer. The cheaters are simple to deal with but Meta-gamers always rub me the wrong way.
Cheaters would always get 1, 2, or maybe 3 columns more difficult on the MM tables.
Meta-gamers were a little more of a challenge. First, I would keep giving friendly reminders that "YOU know there is something behind the door, your PC doesn't." "You, John, know you rolled poorly, but Hrun The Barbarian has no idea what a dice roll is. He only knows that he tried to pull the sword out of the stone and he couldn't do it."
For those players, after several friendly reminders, I change the difficulty for that player.
Player: Well, I know they are hiding there so I'm going to use this door instead.
GM: You open the door and a crossbow trap fires. +75 Range bonus, +25 Surprise bonus only magical DB allowed. +1 severity critical.
Player: I know he stole statuette so I follow him.
(other PC's were dealing with this situation, not the 'difficult player' as his PC was elsewhere in game.)
GM: How? Your character was in the tavern at the time. He wasn't even near the mansion.
Player: Well, I know he has it so I follow him. Can I roll Stalk/Hide?
GM: Sure. The guy you're stalking turns around and looks you square in the eye and says "Why are you following me, you dog? Trying to pick my pockets are ya? Guards!!! He tried to pick my pockets!"
GM: Two town guards approach you as the other guy runs away into the crowd. Their weapons are drawn and they order you to stand still.
I only do those steps after several warnings. I don't want to manipulate the game like that, but sometimes subtle reminders don't work and the meta-gaming takes away from all the hard work and planning I put into the session and the other players who are trying to play their PC's are suffering for it. In the end, I award bonus XP for PC's who stayed in character, even to their own detriment.
Many times I've said "I know there's a darned fire trap there but.... arrgh, crap. I open the door and go in...."