Why are there people like this?

So today, I was in champ select and I am last pick. I got top while this other guy got mid. I selected darius as the person I wanted to play. The mid, who was first pick, then autolocked Darius saying he has an 85% winrate as Darius.

I tell him that he can play radius, but I cannot go mid because I am a bad mid and he agrees. In game, he then tries to duo top until I threaten to report him. He then proceeds to go 1-10 or something and blames me the whole game for not letting him go top when he was assigned mid. Under normal circumstances I would have let him top but if I went mid, we would have lost regardless. I didn't dodge because he didn't seem bad in champ select. Oh man was I wrong