[Irish Wolf]

D&D player who managed to get his young frost giant character(!) killed. The DM let him take over another character. We wound up in one of the dungeons from, IIRC, a Dragon Magazine competition; part of it involved finding a grocery store with a portable UPC scanner. I lifted the scanner, of course. Later, we encountered a library, where we were divided into two teams and challenged to find all the books on a list in the shortest time; the team I was on, of course, won, as all the books were labeled in UPC rather than written language. The problem player's character started pitching a fit, prompting the Librarian to begin summoning powerful assistance. My mage cast Timestop on him, and two others trussed him up and took him outside before he could get us all killed.

The player stood up, punched the host's refrigerator hard enough to leave a dent, and stormed out.

On a more amusing occasion, we had a DM with (undiagnosed) ADHD. At one point my barbarian had found a sword that was smarter than he was, as well as being cursed; once drawn, it had to at least participate in the destruction of a living or undead creature, or it would cause him to go berserk on the nearest target. If there were no monsters nearby, he would berserk on the party. If alone, he would berserk on himself. It's a clue to the character's persona that he didn't see a problem with this.

Our party had aided some powerful extraplanar creature, which rewarded us all with one wish. Each of us, predictably, made a wish that the DM could cause to blow up in our faces entertainingly. At last, we were standing there, trying to figure out how to fix all the things we'd screwed up, when the creature said that one person hadn't made a wish. Turned out he took the intelligent sword for another party member. We began talking over one another, suggesting things the sword might wish for (that would, not coincidentally, help us). Finally, in character as the sword, the DM exclaimed, "I wish you'd all shut up and let me think!" Dead silence dropped across the table as it sank in what exactly the DM had said, and that he hadn't even thought that one through. After a bit of discussion, it was decided that for the next in-game day, none of the characters would be able to speak aloud.