A form of sexually transmitted infection caused from prolonged sheep bladder abuse. The symptoms are similar to Belles Palsy where one side of the face suffers paralysis and noticeably droops. The difference here is that one side droops, but lower in the anatomy. Specifically within the scrotum.
Cooper's Droop aka Highland Wilt is a condition common in the Scottish Highlands causes by sheep bladder abuse. "Seamus is limping again. Must have a wee case of Cooper's Droop."