Years ago I suggested this and rito said no way, in fact many commenters also said no way but they've already done it kind of with the /mute all feature added. This is very simple, add a setting that disables the entire chat for you in-game. This setting can only be enabled disable outside the game in the client so you can't do it in middle of a match. There is no need for chat in-game with the current ping system you can tell your team everything you ever need to. This way no matter how hard you tilt and want to tell people to %%% themselves you simply can't and boom toxicity gone....or well those who still continue their toxic behavior definetily deserve their bans when they could've made the choice of making them unable to flame. This setting should automagically become enabled if you ever get chat restrict or temp ban and you have to go and enable it manually. I can't even imagine how many games there would've been that might have even turned around if I couldn't participate in chat no matter how tilted I got and im definetily not alone with this.
Many of the battle royale games for example have no chats in-game and they're totally toxic free...I think this should become stable for extremely competitive games such as LoL.