When your unwashed ass hairs become matted together and intertwined from sweat and dingle berries. Ass dreads as the tribes native to swampy areas call it. Gorrilla ass is often follwed up with a heavy bout of ass itching, done only through the outside of the trouseres because the smell is so fierce it will stay on any surface it encounters.
After parolling the hot Iraqi desert for weeks with no shower, Sgt. Slapahoe had developed a serious case of gorrilla ass, to go along with his G- DUBS.