It sucks to feel like that. If you can be open about your trichotillomania, then I'd simply say, "I have a condition called trichotillomania." But at the same time, as gimmeice said, it's none of their business, and I like Junerain's advice to tell them they're rude. But my point is, if it's something you can speak up about, you might be able to educate them...some people are open to it.