When you take a major fall off of typically an off road personal vehicle...ex: dirt bike, atv, quad, etc. This could also easily be applied to falling off of anything really...ex: bicycle, skateboard, rollerblades, stripper pole etc.
Holy sh*t dude! Did you see that douche bag try to jump over that dune on his quad? His leg is turned around backward! That was the worst dirt nap I've ever seen!