A poop crayon is a poop that is used to write on the walls of a narrow bathroom stall. This usually happens when some emergency occurs when the poop is part of the way out your bum- you stand up, bend down, move around and meanwhile your half-extruded poo is writing all over the walls.

the thing that you don’t have when you’re phones percentage is over 20

Poop Crayon - (Noun)
A Poop Crayon is a small piece of fecal matter that is stuck in the anal cavity that continues to write on the toilet paper when you wipe. Poop Crayons are extremely troublesome especially when you are in a rush.