From Riot's support knowledgebase:
Do not threaten or repeatedly tell a player you will report them. Doing so can encourage players who are already negative to continue their behavior. Whether they know they are being reported or not has no bearing to whether the system will act on them. But most importantly, repeatedly threatening or arguing with a negative player can end up derailing the game for everyone else and then open yourself up to reports and possible disciplinary action as well. Avoid negative thoughts and useless chatting with poor performing teammates! Focus on victory by muting the offending player and then reporting them at the end of the game.
Do not ask other players in the match to report the offending player. It only takes one report for our systems to review a game. Additional reports will not do anything for the offending player; however as mentioned above, it could open yourself up to a report of your own; especially if you are derailing the match by constantly demanding reports of other players.
In a perfect and just world, everyone who deserved a punishment would get one. In reality, it is possible for some punishable behavior to go unpunished. First, punishments in LoL can only occur after a valid report. Second, punishments take into account the consistency and severity of the punished player's misbehavior: if two players in a match break the same rule in the same way, one who consistently misbehaves in this way might get a punishment while the other who almost never does so gets away without a punishment (this time). At the end of the day, though, all this does is explain how differences in player behavior over many games can produce different results for equivalent behavior within a single game. It doesn't excuse poor behavior. One person having a rare bad day doesn't give a consistently toxic player the right to join in. The only behavior that matters in your punishment is your own... and a good thing, too: how would you feel if you behaved yourself but got punished anyway just because all your teammates were spectacularly friendly, communicative, and positive?
From Riot's support knowledgebase:
We can not discuss other players’ actions with you but you can always report them at end of game and mute them when in game. There is no excuse for raging back or responding to people trying to get you to tilt. You are the only one responsible for your actions and your words which is what we are trying to address with these bans.
