I don't want to help my cousin on homework
Does he have a learning disability, or any other condition that would make it hard for you to help him?
Of course not, It's because he's so annoying to me and I can't stand him.
If you have time, you should help your cousin out. You should do it since he's family, and he'd do the same for you.
He wouldn't!  I'm smarter than he is, and I have better things to do.
If you are truly too busy to help at the moment, then you can take care of other things.  However, it is right to try to help out family members when you are able, especially with important things like homework.  Try to be more considerate next time.