Can I refuse to apologize to my sister after saying hurtful things to her
That's awful. How would your sister react if you didn't?
Very bad, she's told me that I am like a bull in a china shop.
If you really hurt her feelings you should say sorry. It will only cause a divide between you to if you don't.
My sister is a pussy and so is her ex-boyfriend. She can get over it and I'm not going to apologize to her.
She might not get over it and your relationship could suffer. You need to apologize for what you said so that your relationship can heal.