skidmarkalgia 

A disorder characterized by brown streaks in the patient's underwear, usually in the rear. This condition is often misdiagnosed as skidmarks. The difference between them is that skidmarkalgia is typically wider spread and thinner, whereas skidmarks are more centrally located and darker. The exact causes are unknown, however anecdotal evidence suggests that fisting may be the primary cause skidmarkalgia.

“Maybe skidmarkalgia can be induced by fisting, FF, but not fibromyalgia.”-Village Voice

skidmarkalgia by madcow3417 June 22, 2008