A dumbledore is a small portion of poop trapped within folds of the exterior of the anus.
A dumbledore are commonly confused with a dingleberry, which consist of poop attached to anal hairs. Dumbledores are far less dangerous to undergarments than dingleberries, but still poses some risk, and are far more difficult to remove. In fact, the vast majority of toilet paper is consumed removing dumbledores.
Jimmy had no trouble pulling guys at the club, but he never whipped his ass properly, so guys usually got annoyed with getting dumbledores all over their dicks or tongue, and dumped him pretty fast.