Muting 101
You ever get that one player that starts badmouthing teammates after the enemy gets first blood? How this player also starts acting toxic whenever things don't go his way? You feel like muting this player but you feel the need to make him aware. Don't say that the person is muted, just mute the player and move on with your life. All you're doing by saying "muted" is basically causing some sort of anger on another player, your teammate on top of that. Be the bigger man and just TAB>Mute and move on, eventually he'll stop talking when no one responds.
In the grand scheme of things, muting means you don't care what this player has to say, nor do you care if he knows whether or not you know what he said.
This goes out to all the players that feel to need to defend themselves when a toxic player starts harassing you. Is muting the answer to League's toxicity? Absolutely not. But it helps to keep the fires low and unseen. And more importantly, it keeps your attention on the game.