Real women have curves. Real women have some meat on their bones. Real women should be shown in ad campaigns, not those bony size twos — nobody likes cuddling with a bag of bones!
If you have heard any of the statements above you have heard a different kind of body snarking that is fairly socially acceptable, even among people who consider themselves feminists and generally body-positive. Many women feel justifiably frustrated with the uncommonly precise standards set by the fashion and television industry, so rather than taking out those feelings on the establishments and societal norms perpetuating them, they opt instead to criticize models and thin women.
Calling a woman fat is typically considered as awful (well, by everyone except the Daily Mail and Karl Lagerfeld), whereas telling a woman to “eat a cheeseburger” or insinuating she has an eating disorder or critique an actress’ performance based on her slim figure is somehow permitted.