AFKing During the Last 10 Minutes
If a player AFK's during the last ten minutes of the game, because they're salty, it should be a permanent ban. Plain and simple. If you're wasting four other people's time, because you're a salty Riven main, you should be banned permanently. No second chances. No warnings. This has happened to me the last 3 games. The team will do well; one person will get camped, said person makes it their mission to tilt the entire team, then they AFK during game-changing teamfights.
Maybe I'm just a little upset, and a permanent ban is too harsh for said offense, but this should definitely get more attention from Riot. I have reported people in the past, and I have not had feedback saying that a person I reported has been punished.