I had a sibling go to NC with me and I want to insult them.
Are you feeling angry towards them?
Yes I am, he doesn't even care about me anymore.
It is fine to call a sibling out for treating you poorly. Family should treat each other well and you should let them know as respectfully as possible if they aren't.
So I should just let him walk all over me?
No, you should definitely not let them walk out over you and you should absolutely call them out. However, just insulting them won't accomplish anything and will just cause more unnecessary tension and not get your point across.