Why are people in flex queue so toxic?

I don't know whether they are just having fun or not, but after hearing excessive profanity and such in the last game, I'm utterly confused. I can hardly understand why they need to talk so much shit to me when I simply asked why we had an Irelia mid. The top/support duo were constantly flaming me in champ select. In the game, the called me useless (which I sort of was, but sitll that doesn't mean they should flame me) and were calling me bad.

I've never seen this before until I started playing flex queue this season. I really wish Riot would do something about this, maybe make enforcement in flex queue stricter or something.