We went to him and told him to his face he was being unfair to our grades. We insisted he remark our work. When he talks to us he gets irritated and insisting on it he says "I can't help you anymore" and he walks away.
Continuous insisting on this person gets him shouting at you. Me and many people from my class tried to talk to him. He gets angry.
For the explain 'x' and do 'y' I'm going to try the idea of recording what he says. I doubt the teacher would allow it though. He'll put me through hell for the rest of the semester.