Self-muting

Please please please please please please please make a toggle to self-mute that can only be toggled through the launcher or through the website(not in-game). We get put in a competitive environment, which is going to get some peoples' temper flared and then punished for it happening, with absolutely no way to help ourselves not get that way(there is literally none, muting does nothing since your team mates can still see what you're saying).

I'm on a 6 game loss streak, most of which I have early killing sprees(a couple legendaries), I win team fights for my teams, steal barons/dragons, keep wards out, help keep lanes pushing and every game I have carries who dive into the enemy team and get one shot or people going troll builds(sion with stormraiders, youmuu's, and drakthar). How am I not supposed to be frustrated by this?

I know people are going to say something like "just keep it in, learn some self-control", but to those people I would recommend they go to a psychology lecture or read a book on human behavior. It's not just simply "keep it in". If you're going to dole out severe punishments for having a competitive attitude in an inherently competitive game, then you need to make ways to keep yourself in line. In the words of Christopher Hitchens(referring to religion, but it still applies) "You're created sick and commanded to be well." Anger as a result of incompetence of people on your team or even at your own incompetence in competitive environments is human nature.

I can't see how this could take much developer time as the functionality to mute players both in-game and out of game are already in place and I know many players would use it as they behave irrationally during a game and then wish they hadn't after AND these players would no longer be creating a toxic environment for those who don't behave that way.