My dad is never happy with my grades.!?

So my report card just came, and I have four A's, two B's, considering they're both Honors courses, and a C- in Geometry, (it was a D in my last progress report) & Math has always always been hard for me. So, my dad is being such a douche bag because of this. Yeah, I had a 4.0 last year, I mean come on it's freshmen year, easiest out of all. & He even said so! I don't get it. He's never happy with anything good I do in school. My dad was a stupid delinquent kid when he was my age, and my mom never even made it to the tenth grade.(haha) My parents also never got mad at my brother when he brought home way worse grades than me. It's a dread living with these people who are never happy with me. I honestly don't know what to do anymore. Any advice?