Two things
First item:
There needs to be a mechanism for reporting people who become intentionally toxic when they get autofilled into a role. I've seen people actively feed or outright just refuse to communicate with the team when they get put into a role they didn't queue for. There needs to be something to address this.
Secondly:
Riot needs to recognize there are sore winners as much as sore losers, so there needs to be an item to report sore winning under. Like getting ahead and trolling the team and prolonging the game. Then again I doubt Riot knows what sore winning is since they promote borderline bad manner behavior by enabling players to flash mastery emotes in game. In professional sports if a player showboats like that they'd be fined or otherwise censured by their team.