My cousin is gay but i still feel as though he is normal, my problem is my father who keeps insulting him?

by insulting him, calling him a shirtlifter or a poof, sometimes a puddle jumper and on the odd occasion he will call him a fudge packer. I hate it when he acts this way, why must he be like this? I mean it is not my cousins fault he is good with colours.....should i tell my father to stop being a shite