"lol i want to lose cause you dont deserve win" should be insta permaban
there is no reason to give someone a 2nd chance who admitted that he wants to lose on purpose because he dislikes someone for whatever reason. end of story.
if you want context on what happened: our adc was twitch and he helped the jungler with gromp. twitch then leaves, the jungler fail smites and twitchs poison gives him the finishing blow. jungler came bot, gave blue to enemy adc (just running into tower) and said "lol i want to lose cause you dont deserve win you are a fucking cancer troll" after that he said he just afk jungles so he doesnt get punished for afking or feeding.