The shit that ends all shits, a crap so mean that can start the end of the days. The kind of crap that breaks one of the biblical seals letting hell loose on Earth.
Man 1: "Yesterday I went in a McDonalds bathroom and it looked like somebody took a crapocalipse"
Man 2: "What do you mean?"
Man 1: "It looked like a nuclear shit attack, it was even on the ceiling"
1. Crapocalypse, n. Of or referring to a shiat of apocalyptic proportions.
If I had a crapocalypse brewing, and the manager said I couldn't use the bathroom, I'd squat in a corner, mud the place up and wipe my runny arse with the merchandise.