The idea at the core is good and makes sense for people that have temper issues. Where I start to lose it though is how would this work? Do you set in the main client and then are unable to chat at all for the whole game period, or can you toggle it in game? If you can toggle it in-game the seems like it defeats the purpose since you can just turn it off and flame. Worse yet, if you can't toggle it you've effectively gimped yourself in situations like where you ping mia on the river but nobody has wards so they can't see the roaming LeBlanc that just left vision. In those situations its best to say "LeBlanc is definitely roaming bot, care" to reinforce your pings and let your team know it wasn't an accidental ping.
There are upsides and downsides to both ways of handling this. I think the best solution is just self-control. Don't say anything at all except stuff like Mias, spell timers, etc. When somebody tries to start something with you mute them so you are never tempted to respond. That way you can be a team player and not get baited into flaming.
