I'll boot any random that joins and uses the evil smasher glitch.
Kids who try to use modded weapons.
These + the Fibber. Anyone who rushes past all of the enemies just to get to the next area. Ninja looters. Those that start turning unwanted missions in. Those that forcibly travel to a different area. Those that stay in the menu for an unreasonably long period of time while the rest of the party tries to travel to the next destination. AFK people.