Wtf the picture is following my mouse xD.
I use the good ol' mute and report in game. In the case of pre-game / post-game, there's nothing you can really do to stop them. That being said, Riot can and does read both pre-game and post-game chats, so as long as you report them through the in-game system, and give a brief description detailing what happened, and where (IE which chat) it happened, it will be taken care of. Of course, if that doesn't convince you, you can always submit a ticket to Riot Support directly.
I can't stress enough; don't talk to these kinds of people. They thrive on getting under peoples skin. If you want to get back at them, the best thing you can do is deny them what they want, and just don't say a word back to them. Take solace in the knowledge that you will keep you and your account safe, while they just compromised theirs for using a zero tolerance word.
