Or become really nice to people. Little compliments for small or big plays go a long way to developing team cohesiveness, and softening blows to people's egos let them play confidently and, overall, better. A little over half of my ranked wins have involved somebody getting mad or provoking a fight with another teammate, and I've stopped all but one game from death spiraling into a defeat by just being a mediator and, when necessary, the argument ender.
Number one thing I've found, the sooner you can get both sides to just drop the issue with no grudges, the sooner the game turns around. Staying neutral on the argument, but firm on ending it for the sake of winning the game, often is enough to get both sides to drop the argument and just win. They're playing ranked for a reason, and it's usually to win and prove to others that they're good. They don't do that by complaining and losing a game, they do that by shutting up and playing the game. Sometimes they just need to be tactfully reminded of that.
Sarcasm, snark, and outright insults make nobody play better, where as compliments, reassurances, and apologies will make almost everybody play, if not better, at least slightly happier. I have nothing to lose from being nice, and everything to lose from being a jackass.
Also, totally shit stomped a vayne as veigar. Literally blew up their tank from 100-0 by the end of the game.