I usually just say that I can't have most baked goods and pastas... I know that there is so much more to it than that, but I also don't want to give them a health class lesson explaining it all... I get bored of it after a while
Along with explaining my condition in the shortest of terms, I get a lot of sympathy- which I don't always like because I want to feel like I'm normal, not sick! I've also had some pretty funny reactions, like "Oh so you can have cookies, but not the dough?" Uhhh, what? They then said that they thought all the gluten "baked out." *facepalm* Gotta try to understand though, most people don't even know what gluten is, I know I didn't before my diagnosis.
If you find yourself being pressed with all kinds of inquiries that you've heard 1000+ times, or find yourself being the center of attention when you don't want to be, I would just try to change the subject. I've had plenty of times when I've wanted to say, "Just STOP asking me about it, would ya??? It's not a big deal, okay?!??" It would probably feel good at the time, but I'd totally regret it and feel guilty later!