I think younger people are more likely to understand the term large intestine than colon. I would say something like "My body attacks my large intestine. It's like having food poisoning all the time." (good one handfulofrain). especially because then people will be like "Do you throw up?" and then you say "no..." and then they know you mean diarrhea, but, like, it's not your fault for being gross because they asked.
Most people, even teenagers, can relate to food poisoning. For a colonoscopy you could say that they use a camera to look inside your large intestine. I am all for telling the unvarnished truth but teenagers are immature a-holes, if you mention your butt they're just going to laugh instead of being sympathetic (some people my age are this way too
dx'ed UC pancolitis 5/12
past meds: asacol hd, VSL#3, apriso, rowasa, xifaxan, 6mp, cortifoam, pentasa, cimzia, canasa, butyrate, flagyl, cipro, prednisone, remicade, methotrexate, cholestyramine, cortenema
current meds: none!
step one: colectomy, end ileo 1/16/13
step two: j-pouch construction, loop ileo 5/1/13
step three: takedown 7/31/13