"How do you manage to eat so much and still be so thin?"

This is the third blunder!
Why?

Translation: I am so obsessed with my weight that I can't believe that there is someone who isn't secretly thinking about their weight all the time. I can't stand the sight of someone thinner than me eating, so I will continue to hound you until you confess to being bulimic / a junkie / in the gym for the 23 hours a day you aren't eating in front of me. I will comment about it any time I see you eating, and if you try to avoid eating in front of me that will just prove that you are anorexic, so I can then give you superior, 'concerned' looks. I can't accept that some people are just thinner than others, in spite of scientific, and indeed visual, evidence to the contrary, as I get all my information about such matters from 'women's' magazines that rely heavily on advertisements from the dieting industry and therefore don't want to encourage women to be happy with, or even resigned to, the size they are.