Ghost Riding the Whip [wiki], or simply ghostin' is a hip-hop car stunt in which the driver gets out of a slowly moving car to dance around and on top of the vehicle.
Apparently, it should also be called "thinning the herd" or the "Darwin Awards dance":
“Ghost riding the whip” — a stunt in which a driver gets out of his car and dances around and on top of the slowly moving vehicle to a thumping hip-hop beat — has gotten at least two people killed, led to numerous injuries and alarmed police on the West Coast and beyond.
A fad among devotees of a West Coast strain of hip-hop music called “hyphy,” the stunt has been celebrated in song and performed in numerous homemade videos posted on YouTube.
“It did not take Einstein to look at this thing and say this was a recipe for disaster,” said Pete Smith, a police spokesman in Stockton. “We could see the potential for great injury or death.”