My parent thinks I am mentally ill?

I've got a father who many people claimed to have some sort of slight anger problem. He will get angry at almost any mistake anyone does. Since I am the only person who lives with him it is no mystery that I am the most frequent victim of his anger problems. Usually he will start to shout at things I do wrong, then continue to exaggerate the problem and then link the current problem to the previous mistakes I have done in my life. At some point he will break loose and becomes extremely abusive both mentally and physically towards me. What bothers me more is that he thinks I am mentally ill to a point where I am no better than a 7 year old (I am 19 yrs now and in uni). To him, any mistake is intolerable and many of the times I didnt even make a mistake, but merely a misunderstanding by him.

Normally when he wants me to do something he expect it to be done FAST. Immediately. Any delays in thinking about how it would be done is disastrous, esp if he is in a bad mood. This pressure forces me to react quickly but often at times do incorrect things without even thinking. He then finds excuses to say I am mentally ill. I tried talking to him but it was like talking to a wall, as he is 'always right.'

I have tried prove to him i am not stupid. My grades show that, A's all the time and medals and awards in piles. I've done many of those online IQ quizzes and consistently get over 120. I'd guess IQ is a measure of intelligence, yet that does not convince him at all. He would simply say, 'you are OK in some areas including intelligence but in the more ordinary everyday things and thinking skills your brain doesnt work to standard.' I just love how he can always make up things that aren't possible. In front of any other person on this planet I've met, I behave normal and there is no indication that I am stupid. I just dont know how to deal with him anymore, he wont listen and nothing can convince him, even a proper psychiatrist report of my mental assessment. What should I do?