yes, i have had it happen to me too. As well as the smoking comment. Depending on who is saying it and what mood I am in that day usually determines if I go into detail about CF. Sometimes you just dont have time, or not in the mood for a bunch of questions...and honestly, it's not everyone's business. I am pretty much and open book about my CF. However, that is to ppl I know I will see more than a quick pass in the street. If it is some random stranger at the store who comments on, let say my cough, I really dont feel the need to give them the details of my life. I usually blow it off as allergies or something irratating my throat...they dont know the difference and usually drop it. I am a private person, overall. I think my CF is my business and I feel that I should share it with who every I want to. I do not think it is my responsibility to educate everyone I meet about it. Other ppl with CF will disagree with that, but everyone is different. If something hurts ur feelings, there is nothing wrong with it and it doesnt mean u need to spill ur guts about ur personal health...unless u are comfortable with it. I dont think someone should totally hide their CF (especially in relationships), I think it takes too much effort to do that. It's all up to the individual.
Anyway, back to the question at hand. Yes, I have ppl ask me why I am so skinny or why dont I eat more. My DH, Friends and Family always tell me "I love to see u eat". But ppl who don't know very well, then I wll tell them that I feel better eating smaller but multiple meals in a day, I ate big breakfast, or I do eat all the time, I just have a fast metablism (sp?)...that usually gets the reaction of "I'm jealous" but that is a whole different annoying issue. If they are ur friends at school, and you feel comfortable, then tell them about ur CF. You dont have to go into scientific detail, but just explain that you cant digest ur food that well and have to take pills to help you with it, therefore it's hard for you to gain weight. Go into the lung involvement if you want.
I see this post is back in 2/07. You have probably already handled this, but I'm gonna post my answer any way just in case someone else might be going through the same thing.