1) Rubber that has been scorched into the road due to the heat caused by friction from someone's tyres when either they brake too hard or have accelerated too quickly from a stopping position and caused a 'burnout.'
2) Stains left on underwear due to poor anal hygiene which indeed resemble the tyre-marks scorched into the road.
2) MOTHER: "David, if I find another skidmark in your underpants when I come to wash them, I'm gonna come up there and wash your arse myself you little shit!"
2. the thin brown line in your undies, especially tightie-whities, caused by insufficient wiping
2. Quit acting like a total skidmark, fag!
Also presents in a less structural (and lesser known) form, typically developed from excessive "dry farting". In this form, the skidmark develops in a larger region, yet its definition is not as clear. Essentially, it is representative of a consistent gaseous pounding of one's underpants over a long period of time, and while fairly rare, is unmistakable. Usually, this effect is understandable to about 1/10th of all humans.