Smurfing
This should be considered bannable. I'm not sure about anyone else .. but when you're pit up against a diamond smurf as a silver/gold actual player, and your lane is just totally shit stomped ( I was adc) it's a little ridiculous. And all they ever say is "smurfing is fun". It ruins the game for everyone who plays except the ones who are completely kicking ass. Teams need to win because of their current skill level, not because they got carried by some guy that's considerably better than the rest.