why is it.... [people telling others when they are not feeling well]

OK, good, so can you cover for me if I take vacation time next week?

Smokers, for one.

A bore is someone who, when you ask them how they are, tells you.

(Possibly Ambrose Bierce, I can’t find a source at the moment.)

Ha! I didn’t think of it until you mentioned it, but I think I have actually coughed before and subsequently been asked if I was a smoker (which I’m not). Good point.

Your answer: Just idiopathic rhinitis.