Thankfully, ive never had problems this bad.. this thread makes me feel fortunate for my group.
We're all long term IRl friends.. we havent played with a stranger in a long time, all of us know each other.. we're a fairly closely knit group and we play the game for fun purposes. We've had nothing worse than occasional arguments.. but the GM has enforced some things that keep it covil (no evil characters in his campeign, no stealing from other players, etc).
nyway.. a number of years ago, maybe around 5.. we used to play our D&D in a local community centre where we rented a room. Since it was at a community centre and registered as a club, we all met each other through it.. it used to host two groups, but the elder gamers left to play at one of their houses, leaving just us. Anyway, for the first time in over a year someone new wanted to join, it was a kid of maybe 12ish years old (we were all late teens to early 20's at that time). We let the kid join in our D&D group,he rolls up a barbarian and we start playing. However it wasnt long before the kid starts acting extremely annoying. He stole snacks, grabed other peoples property that was lying on the table before them. Even took peoples mobile phones and started playing around with them, really annoying and rude stuff. Thing is, he was young and none of us wanted to confront him, but it kinda broke over when one day he tried to take my friends phone.. i'll just call him D, who was a martial artist, one of the older players at about mid 20's and probably 6' 6 or something. Anyway, he crushed his hand into the table when he reached over to take his phone, D had had enough. The kid was real quiet the rest of the night.. he left early though. We agreed that the kid had to go that ngiht. Next week one of us confronted him about it and said he wasnt welcome anymore. The kid burst into tears and ran out, never saw him again.
Thats about the worst thing thats happene din our group. At times a player has gotten really aggrevated by rolling unluckily or failing saving throws.. arguing and bitching loudly aabout it. I got really upset whe my druid who was grappling a downed humanoid almost got hit by the groups fighter (who had no need to attack thegrappling creature) and argued about it and got a bit upset.. but nothing like the stories here.