How thin is too thin?

Recently I had . . . let's say. . . a 'heated discussion' concerning the thinness of models. Now this topic is not about how models portray an unrealistic 'ideal' for girls, or how our society promotes this same unrealistic 'ideal' through advertising. Those topics require pages upon pages of text. This has to do with the phrase "She's too skinny, she must be anorexic!" It's about prejudging an individual without knowing anything about them. The models I photograph tend to be on the thin side, but there are many factors that contribute to thinness other than an eating disorder. Just as it's unfair to criticize an overweight person on first glance, so too is it unfair to criticize those of us who are on the thin side. Yes, I am including myself in the discussion. I have been thin my whole life, did everything I could to gain weight only to hear people say 'Why don't you eat a sandwich?' Years and years of this wears on you, just as it wears on someone who might be overweight hearing the opposite. But people don't see it that way, they think it's fine to joke at your expense because the feel that being thin is the 'ideal'. But I see it in a models eyes and posture when someone all too frequently spouts off 'Wow! You're so skinny!' Most don't take it as a compliment. Just as the phrase 'Wow! You're so Fat!' wouldn't be taken as one either.