just every time your friends come over ask their grades in front of him(Im assuming you have lots of friends that aint genius' lol) and ya ask why the fuck you have to get straight A's??? or take a different approach and keep telling your mom how your dads constant nagging and disapreciation of your grades is lowering your self-esteem(doesnt have to be true lol) and pretty soon your dad should feel like shit and eaze off