i used to be super skinny up until a few years ago and you wouldnt believe how many men told me taht i had the perfect body. its sad. and by super skinny i mean im 5'7" and in my senior year of high school and freshman year of college i was 107-110 lbs. and now that ive gained weight, im about 140 lbs now, ive actually gotten comments (from men), saying how i need to tone up".
im working on losing some weight now, 10 lbs would be great, 15 would be ever better.
but my overall point is, if its not your body keep your mouth shut. you never know how someone will react to your comments, even if it is merely out of concern. and their reaction could be negative.