Raging

flame them out loud irl, not in game(this is good for people with anger issues.) you can't be reported if you do or say nothing to them. or just mute them, also works.(if you have manageable anger issues.)

Don't play League.

It is just a different iteration of "don't cry over spilt milk". If someone is bad on your team, you can't fix it. At least not in the time you have together. Maybe you can give some minor tips to minimize their impact on your team a bit, but not everyone is going to be receptive to that. Worry about your own play. Even in a losing game there are always things you can do better, focus on that. It will serve you much better. That bad player is going to be different everytime, but you will be in every game that you play.

Tears don't clean up spilled milk. Rage doesn't make bad people good.

Listen to Taliyah's login theme, while playing League. This sh*t is so relaxing and pushing at once, you can't be mad anymore but instead, you enter mental godmode.

Get off the game for a while, take a break, and come back to it when you're feeling better.