Its really sad that someone won't say anything all game, but as they are about to win talk all the shit in the world at the end of the day. If I put there names in the post can we have a serious look at them? They don't deserve to play the game or let alone be allowed to rank, but nothing will be done because they talk in after game lobby and no one watches or patrols that.
If they're "talking shit" in-game and are essentially exhibiting negative attitude, just use the post-game reporting system to report that player. Player Support, quite frankly, doesn't have the resources to deal with players manually reporting other players for something that their automated system is responsible for handling. Your report will trigger a review of the chat logs for that match, and if the system determines that the player has exhibited behavior that is contrary to the community standards, the system will either flag the account for punishment if the player continues to be toxic or the system will enact the punishment, having established that consistency already.
Even though Wuks already answered to some aspects of your post, I believe he did not answer the question in the subject of the thread. I try to do that; I believe you mean that if you tell the names of the bad people here in the boards/forums, would that help. Maybe, but (and it is a big but) you aren't allowed to do so. There is a rule against "Naming and Shaming". Thus it would only get yourself banned from these boards/forums.
There are two correct ways to report people for bad behavior; first is the easy after game report. Second is the harder report via support system. The effect of those reports is mostly invisible to us regular players though. You might get "Someone has been punished thanks to your report." message, but more likely you won't.
Riot is also able to see pre/post game chats.
Just write in your report notes that the toxicity is in post game chat.
They'll actually take down your post if you mention names. I did that once. They say to just do the report. Just have to hope you never see them again.
