Men are sometimes clueless, but I don't think they're stupid.
Do you ever think any man was dumb enough to actually call his girlfriend/wife/significant other fat? I'm not talking about a trap question made by the woman... "What do you think of my new jean? Lori says they make my ass look big." That is a trap.
Do you think a well meaning, good man has ever come out and just a flat out said, "Wow, you got fat!" Yeah I'm not so sure... unless he means "phat", in which case I need to find a time machine and send him back to 2002.