When a rash develops around the anus as a result of profuse sweating caused by playing a gig. This condition generally effects drummers due to the friction and sweat buildup around the anus in conjunction with performance. Diagnosis can be determined by evaluating symptoms such as, redness, swelling, itchiness, and severe stench that tends to remain long after showering.
"Did you hear? After the gig Friday night Steve got a really bad case of gig butt. He was caught with his pants down scratching his ass in the dressing room. His roomates say the smell is so bad that they are going to ask him to move out if he keeps playing the drums. I am so glad that you never slept with him. Gross. If he keeps it up pretty soon he will get a nasty case of Swamp Ass."