Disable All Chat
I know I know, we all love /all chat.
But if we're honest with ourselves, it does MUCH more harm than good. Let people /all chat before minions spawn and after the nexus explodes for the "GL"s and "gg"s. At least test it in Bronze and Silver - can you imagine how much flaming could be avoided if you ensured that people couldn't engage the other team? No more "report so and so" or "gg, this mid is noob" or any of the other nonsense that serves absolutely no purpose.