I'm going to insult my aunt to defend my other aunt
Why do you want to insult your aunt?
she's a bitch and an impolite bastard.
Your aunt must have been very rude, but you shouldn't insult her because of it. Be nice to her and maybe she'll decide to be a kinder person also.
I should just spit in her drinks
No, that is even worse. You are an adult, as is she, talk to her and tell her what she is doing is wrong.