Freestyler said:
When you can't see any ribs in the mirror (just subtly).
< 1985 called...they want their definition back. Now-a-days, if you're not obese then you're not fat.
The "Fat Boys" rap group of the 80's would be considered a little plump by today's standards. They were fatter than average, and the average was semi-healthy.
I totally agree with you, freestyler, but society doesn't. Standards have lowered and they don't want to be reminded of the day when the standards weren't as embarrassing. In 2010 America, fat = obese. If trends continue by 2020, fat = morbidly obese.
So, to answer the OP's question, fat is looking more unhealthy weighty than the average of the time.