How many times have you seen one player flame another and then they afk or start griefing?
How many times have you been the player who flamed someone else for an unfortunate gank or they got caught out, and then they afked or started running it down lane?
How many times were you the one who got flamed and so you started griefing or afking?
We can't control others but we can control ourselves. If you want less griefers and trolls then stop setting them off. I know that isn't fair to you and you shouldn't have to put more effort into being mature than them, but you have no real other option.
You win by adjusting your strategy to win.