A poop stache is the remnant hairs or ingrown hairs that are still visible on a guy's upper lip even after they shave. No matter how many times they shave it still stays there. A poop stache is most noticeable on guys who grow hair mostly on their upper lip and nowhere else on their beard or sides of their faces; this makes it look even more like shit.

Literally everyone, ever. Including the writer of this definition.

A thin, weak, fine collection of hairs on the upper lip that is noticible but not technically thick enough to be considered a real moustache. They are usually found on pubescent boys aged 13 to 16 whose moms won't buy them razors.

When you have poop on your upper lip like a mustache. You can have many types of poopstaches in the form of a traditional mustache- like pinchers, goatee, soul patch, etc.