Tbh, this is what I think riot should do: When I mute someone, all their messages are instantly deleted from my chat. That means when I am told to kms, after I mute them, their message won't stay there taunting me. Secondly, they should stay muted in the post-game lobby.
OP, don't add someone after they were toxic to you all game, that's basically just instigating.
Half the time I see someone being toxic in chat, I'm not even mad at the toxic person. I'm grown up enough to just mute the toxic person and report them after the game. The people that annoy me the most are the ones that continue to talk to and instigate the toxic person. People have lives outside of league, and sometimes they take their anger out on the people playing with them because they have no other outlets. It's sad, but you can just mute them and let them scream to a wall.
I don't know what I'm saying anymore TL;DR: Just press the mute button and report them, it's really easy. Riot should seriously add some features to the mute button though, like deleting all messages from that person after the mute.
Don't get mad at Riot because they don't have the best punishment system in the world, literally no game does. Everyone complains about every single punishment system. Overwatch, League, WoW, Battlerite, HoTS, Steam, etc. Y'all are acting like if you complain about cancer enough Riot will cure it. Just be glad they no longer have RiotLyte, I hated that dude's system. It was literally just punishment with no reward and we had psychologists on the boards literally telling him his system didn't make sense. I've seen a noticeable drop in a certain type of toxicity in league. I haven't had someone rage at me in a long time. I don't know if it's because I'm not in low elo (I get that gold isn't high elo but like still it's in the top 15% of players) or because I actually use the mute button, but like I just don't think we should be complaining about league's report system anymore.