When something tastes so vile, so disgusting, so repugnant, that it can be compared to what a butt might taste like.

(Of course, most people don't taste butts, so a better phrase would be "what a butt smells like." Or, perhaps, what the expulsion of methane from out of the butt smells like.)

When you eat dirt for the first time and leave your family to build a shack in the woods