This cunt was friendly to the table next to mine, but not to me, so if her double standard is ok but not mine

No, I'd say this piece of information changes my opinion, I think I missed this in my first read, it was your other reasoning I don't agree with. But if she was less friendly to you than other customers, thats rude, and a perfectly good reason to tip her less imo. You deserve the same level of service as anyone else