is it fatphobic to get mad/sad if someone calls me fat?
Depends. Are you thin?
Because if you’re thin, I can understand being mad at being called something you aren’t, but being fat isn’t a bad thing and it isn’t really much of an insult. And I don’t think you should care so much.
If you’re NOT, though… well, you probably have lots of trauma associated with the word and how people treat you because of your size. So it’s absolutely understandable to be uncomfortable with it.