Toxicity outlet
Ever since beginning this game, I've never been that toxic of a person. If a person is doing horrible, but tries calling me out, I'll normally say something along the lines of "1/5/2 with 42 cs at 15 minutes. Sips tea" and that's as far as I've been.
Ok I lied one time someone made a really horrible pun and I said "kys", but that was just muscle memory from how I respond to my friendly with their stupid puns.
But, some people REALLY piss you. Like just REALLY know how to get under your skin. But get this. Instead of flaming them, I write down whatever grotesquely vulgar statement I please and then press Esc instead of enter. It's a really good way to let some steam off, without affecting another player, how they play or the match.
To anyone struggling to not be toxic, I recommend trying this method out. Muting also helps too, but it's w/e. Do both.