I've had so many instance like this. When I was a freshman in college a couple years ago now, a friend and I were going through clothing another friend wanted to get rid of. The friend getting rid of stuff pulled out a pair of pants and said they were too small for her, the other friend said they were probably too small for her too but would probably fit me because I had the thinnest legs- and yet I had always considered my legs to be the thickest!
My other friend was saying how she wants to lose weight, and I mentioned that I'd like to lose a little bit too. Her reaction was, "But you're so tiny!"
But of course, I have another friend who has called me pudgy -_-
I hate how distorted our self perceptions are. I think it's a mix of things though- being hard on yourself and also mirrors flattening images so it's hard to tell what you really look like.
This site:
http://www.mybodygallery.com/index.html
is nice too, we need to have more women of different shapes and sizes in the media. Skinny and narrow hipped is not the only body type!