It's better to say nothing.
After Riot Games added the new party feature with Patch 13.4, League of Legends players were thrilled as they hoped friendly bantering and trolling would make a return to the game. Unfortunately, the community learned the hard way that party chat is also susceptible to all penalties.
Recently, Riot started introducing stricter punishments for leavers and toxic people, restricting their access to chat and punishing them more severely. As a result, players reported unjust chat restrictions.
With party chat coming to the game with Patch 13.4, players thought theyd at least be safe from chat restrictions and similar penalties in their party chat, but it turns out party chat is equally susceptible to penalties as team and group chat.
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According to a post from Leagues subreddit yesterday, if you banter with your friends in party chat and a random player in your game reports you, you might get a chat restriction.
So, players are slowly turning away from chatting, saying the best practice is to not use the party chat as you never know what can get you banned.
The entire system sucks to be honest, as most chat autoban features always do. The fact that you’d get chat restricted for saying something to a friend in game like ‘yeah my mom just got diagnosed with cancer, I’m bummed,’ is just asinine. In a game where an optional mature language feature already exists, there’s really no need to censor the players actively in game. You can already do that as well by muting someone. It’s just such a waste, one player explained.
Nobody actually knows if this was intended or not, but in any case, its best to avoid using strong words in your party chat because you never know what can get you banned.