On one hand the real insult is someone calling you fat or badly proportioned. But on the other hand, a lot of people think fat butts are sexy. I'm not even going to put "now" at the end of that sentence, people have associated big hips with fertility and good genes for hundreds of years, if not thousands.

Personally I think the whole "big butts are bad" mentality is purely an American invention from within the last 100 years