I had a male friend in college that was over 400 pounds. Guess what we called him, Fat Nick.
You will never hear women refer to a member of their friends group as Fat Maddy.
A fat man knows he is fat. He does not delude himself into thinking otherwise. He accepts it and often does not even mind being identified with it. A fat woman, on the other hand, is anything but that. She will refuse to see herself as fat and will be deeply offended should anyone address her as such. In fact, if you attempt to tell her she is fat, she will take offense and quickly label it body shaming, as though her weight were an injustice inflicted upon her rather than a condition she helped create.