I'm going to call my dad a meathead.
Why would you call him that?
I think he's an idiot, and he's always disappointed me.
Even if you dislike someone, intentionally saying something to hurt them will not help you at all. It will just make them feel bad and will make them dislike you. Especially since it's your dad, you should be kind and respectful toward him.
It's fun.
It might be fun for you, but it would be hurtful for him. I hope you can understand that.