A.K.A. Saggy crotchitis. Happens when you wash your underwear in the inappropriate temperature of water and/or dry it when the label CLEARLY states "hang to dry". It is characterized be a very tight elastic waistband and embarissingly loose fabric. It is also accompanied by the sense of "I shouldn't have eaten that extra Chimichanga...."
Don't worry buddy its not your fault, its just a common case of sag-cro. Cure? Scientists are working hard, but nothin' yet.
Zeek opened his girlfriends cabinet only to find all of her
underwear had sag-cro, he broke up her later that night.