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.
1) "Whoa dude, look at that
skidmark in the road! Someone must've had to brake to avoid that
ominous pool of blood next to that body there."
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!"