Do all women secretly want to be super skinny?

Women go on and on about how they feel comfortable being a certain weight, so why do they get all ratty when a super skinny woman comes along. I just happened to mention to my girlfriend (who is 5 ft 6 inches about 9 and half stone) about a woman I work with who is super skinny, (I even said I thought she was sickly skinny), but this seemed to make my GF all insecure and she got quite ratty for the rest of the evening. Personally before I get my head bitten off, I find all womens body shapes attractive.