When you shart, and and the blood from your cancer and/or rectal infection turns the poopy soup into a tomato flavored red paste, like ketchup.
Origin: While playing I was playing Pokemon (cause I'm a beast), my brother tried to say "Ash Ketcham," but failed like a woman. Naturally we made it into a word.
Chaz- *farts nastily with much gusto* "Aww man, I think I just made ass ketchup... Darn cancer/taco bell."
Bob- "Ever since Todd developed that digestive disorder, the only thing he has had on his burgers is ass ketchup."
Richard- "My name is long for dick."