I care not a wit for FP's weight but he has a terrible character. He is mean, insulting, arrogant and hypocritical. None of that has to do with his appearance; his soul is foul.
This.
But especially this :
his soul is foul
I think deep inside he is a really sad man, but since he looks like he does, the arrogance, the hypocrisy, etc, is just a defense mechanism to keep him from having to actually take a good look at himself, at the way he acts, how he speaks, and the person he really is.
He acts smug, superior, and arrogant because he feels if he puts himself above us, he can tell himself hes better than us and that's why the insults don't matter.
The only real thing his self esteem is based on is his intelligence, but he cant even face the fact that hes just not as intelligent as he thinks he is. (1st thing any person that is even midly intelligent will tell you, is that they dont know shit. The guy that talks the most, almost always knows the least.)
This is also why he desperately tries to prod people that get under his skin to post a pic, because if they don't he tells himself that they must look worse than him, and if they actually do post a pic, hell just try and tear their pics apart and point out all their flaws, again keeping himself from looking at the sad reality that is his own body.
Textbook deflecting the attention away from himself and trying to make it about the other person. Rather that deal with his own emotions, he just tries to attack his tormentors. Hes like a walking sociology lesson.