Currently, the gaming group is rock-solid and well-mannered.
In some of my past gaming groups (of which, only one person, my brother, is still around), that was not the case.
In the 1e/ 2e days, we had a player that was a notorious feud-starter. When we gained two new players, he decided to engage in a competition for allegiance. He swayed one of them to his cause, while the other newbie did not. He then came up with a ridiculous plan to lure that PC to a secluded spot and ambush him from afar with bow and arrow. Didn't work, I might add.
The same player later came up with a plan, which he told in detail, to assassinate the other PCs. It involved a hiring a half-dozen assassins, drowning (!!???!!!) a magic intelligent sword owned by one of the PCs.
His antics eventually spilled out of game and he ended up getting into a fist-fight with another player. We made him take a leave of absence until he cooled down and came to his senses. The only reason we didn't stop gaming with him permanently was because he was one of the original gamers from the group.
There was plenty of inter-character conflict when we played Vampire, but I always figured that was par for the course.