the crusty and flaky substance that forms between a persons ball sack and butt hole. The substance often secretes a foul smelling odor. In some cultures it is a symbol of dominance for a male to force a female to eat the scum off of the male. This has also become a popular act in College dorms throughout the United States.
Hey fuck face, every time you sit on the couch naked you leave a pile of grundle scum.
by XPC-Sacramento November 05, 2010