It usually happens like this:
Unsuspecting Acquaintance: Hey, Maggie! You want some of this food/You want to go out tonight/Some other completely innocent question?Read more »
Me: Thanks so much, that sounds great... but I can't. I'm not feeling too well.
UA: Oh, bummer. Are you sick?
Me: No, well... Uh, kind of.
UA: *concerned look* Are you alright?
Me: Yeah, I'll be fine. I just have this weird chronic disease thing that's been flaring up. It's called Crohn's Disease.
UA: *concerned look becomes slightly panicked* Oh, wow. What is that?
Me: (Give my go-to explanation of what Crohn's is and how it effects me, usually as succinctly as possible. Trying not to make it sound too bad, but still give an accurate representation. Not so easy.)
UA: *no longer panicked, but still vaguely confused*
Me: Also, I've named my colon. It's called Myrtle. (Okay, so I don't really say that. Maybe I should try it. Might break the tension a little. *mental note*)