A bloody shit disease....quite literally. People who suffer from this non-infectious disease usually end up spending lots of time wrapped around the loo with bloody diarrhoea during flare ups. Caused by person's immune system attacking large intestines lining causing inflammation and ulcers, loss of appetite and generally feeling like utter crap. Medication can usually help to control it though some have awful side effects such as moon face
Stuart: "hey why did that hot chick run off to the loo so quickly?"
Bob: "Ahhh she's got the ulcerative colitis shits, she's going to be a while..."