You need to report them, And trolls will be trolls, can be eradicated, simply by placing a report in the client. If their behavior is over the top, for instance. Someone told me today, they hoped i died in a car crash tonight. Then using the match history, riot provided. Put a support ticket in under account management. If they are that cruel when you don't even say anything, then you mind aswell fast track their account being reviewed. I've had friends, in real life. Get banned for their unsavory behavior on league. They didn't quit the game, but when they realized how much time and money was lost, for something they could of avoided. They changed, or "reformed".
Trolls want to be trolls, then send them back to CO-OP AI, let them lose's any merchandise in game, and I guarantee you they think twice before trying to do something that negative. Its not the community, its individuals in the community that create player response's, you need to put some time in to remove them from the game. its not all riots responsibility, since its a community driven game.