I want to call a rude girl fat after wasting my time
Why do you think that calling her fat is okay?
She was being so rude to me.
I understand she was being rude but you shouldn't resort to petty insults. Just walk away whenever someone is being rude to you.
I'd rather upset her so that I can have a good time.
You are not going to feel better about hurting her feelings. It is not okay to call people fat, or throw insults at their appearance.