Hostage Taking - The Worst Form of Trolling
To be honest there are many ways that players can be toxic. Through feeding, chat spamming, raging, ping and emote spamming, and more. Yes, you can mute these players ability to make noise, but there is absolutely nothing you can do to stop them from doing many other forms of griefing someone.
The absolute worst? Tends to come from 2-3 man premades. They will purposely hold their team hostage (unable to surrender), while intentionally being toxic the entire game. This needs to become reportable, and bannable, if possible.
Example:
Gnar: Has quit the game. Kallista: "He will be back." Xin and Kallista: Face checks enemy team five times in 3 minutes Lee Sin: "Screw it... FF. They are already 15 kills up, and it's only like 6 minutes in."
Kallista and Xin vote no.
Gnar: Has reconnected! (10 minutes in) Gnar, Kallista, Xin: Endlessly facechecks other team. Gnar, Kallista: Raging at Lee and Veigar, who now want nothing more than to leave Lee: Continues to try to FF, guards the nexus when possible against a horribly fed enemy team. Kallista: "Report this Lee, he's not playing with us."
Holding people hostage in the game is a highly effective method to troll other people, and there is absolutely nothing the player(s) being held hostage in the game can do about it. There's no punishment, either. Invariably they attempt to get the other team to report one of their teammates, and occasionally it works.