As a supp main I know how it is. Personally I go first strike muted, second strike roam to other lanes, third strike I start taking CS and try to carry instead. Not ideal, but I don't see what can be done except maybe bringing back the tribunal. Toxic players can be found at every elo and with all kinds of skill levels, so getting people doing bad away from the game won't do that much. And people are always quick to find scape goats for their own mistakes, specially if they're backed by a premade.
But I'd personally rather have somebody feed their butts off than somebody turning into a keyboard warrior and thinking they can go around berating people just because they got a good score. A week link can always be carried, but a toxic player destroys team morale and soon nobody wants to even try to play anymore.