Something I have found even worse than swearing is, when you're in a multi-player live session and another player, who is supposed to be on your side is killing his own members! Has it happened to you, how does it make you feel? It makes me feel both annoyed and frustrated, with little or nothing you can do to prevent it. Even voting someone off isn't always an option, if you can't always tell who the culprit is.
So what can you do about this...nothing. I know people who ~ because of this ~ have stopped playing online games altogether.
If it's part of the game to do such a thing then fair enough. But when it isn't, they are just spoiling it for everyone else.