Well more often than not, some random tried to Captian the team, and picks people at random to force into support roles, and gets turbo pissed if they themselves are asked to switch. They then spend the remainder of the match(s) harassing anyone that asked them to switch, and making them feel bad for pointing out that they should also consider supporting the team as opposed to not doing so.
Then there are the elitist who constantly blame the team for failing them, regardless of how much they have put into the game.
And the hate some people have for some heros, holy shit. There are tons of people who are "You have to play this hero on this map" or "why re you playing this hero, pleb"
I mean, its nothing new. But holy shit, the intensity is a massive jump form matchmaking.