In one of my campaign's we sort of just turned on each other. First while we were fighting these two dragons that were sort of kicking our asses one of our group, Mao decided that he liked the dragons more than he liked us so he started fighting with the monsters. He shot one of our people in the stomach. She was a fellow rouge and a friend of my character, because of some previous story thing she was pregnant and due to some very nasty critical failures she ended up losing the baby and becoming paralyzed. Then my character Hadrian and Mao had an intense fight the end of which saw us both unconscious. While we were out our resident wizard cast a spell so that when we came to we couldn't harm each other (the paralyzed girl had to get a new character) so we continued on like that for awhile, until we ended up trapped in a labyrinth. The spirit of the labyrinth offered to show us the way out but instead of accepting Mao tried to use an ancient ceremonial staff to seal her away and steal her powers. She staying in the staff for about a turn before it shattered at which point she melted two of our group (including Mao) she tried to afterwards (and a number of very intense apologies that could have gotten us killed had they failed) the spirit felt bad so agreed to revive our the two dead characters. She failed to fix the first one and managed to reconstitute Mao as a one pound blob of flesh that for the rest of the campaign scooted around the floor bashing into things.