I’ve heard all the “what are you, anorexic?” comments as well. I agree that telling someone how skinny they are is just as dumb and insensitive as saying they are a tub of lard.
However, the important thing to keep in mind is that most people don’t understand how that could be seen as rude and insensitive. We live in a society where being thin is not just a health issue, it is the ideal standard of beauty. It’s a standard that is perpetuated by the media, and it’s completely unfair. Unless this beauty standard changes, many people will continue to believe that skinniess=anorexia, even when it’s just a person’s natural body type.
That’s why I take comments like that as neither an insult nor a compliment. I just shake my head and move on.