What do you do if your cousin really really really hates you so much?

As long as your cousin is not harming you or threatening to harm you, let it be. It would be great to be liked by everyone; I don't know a soul who is. If your cousin is harming you or threatening harm, you have to tell your caregivers. Bullying has to be addreased head on, or it will continue. If you are harming or threatening to harm your cousin, stop it. That will lead you down a long road of trouble.