I'm going to call someone fat after they called me weak.
Why do you want to respond like that?
To get back at them for calling me weak.
It's wrong they called you weak, but that doesn't make your response right. It would make you look stronger if you brushed off their insult and did not let it affect you.
I just want to make them pay, I think I'll kick their butt.
Physical violence is not the answer either. If you have anger management issues, you should seek professional help for that. Call your HR and let them know you need a day off for some counseling.