The act of taking a shit really quickly. Named after the Megadeth song of the same name, which is, coincidently, shit.
"Oh no, she's coming round in three minutes!"
"You better take a high speed dirt"
its on countdown to extinction, track 8 is called high speed dirt
The title refers to what happens to a skydiver when his parachute doesn't deploy: you hit the dirt at very high speed and most likely die.
Oh man, his parachute didn't open. Prepare for some high speed dirt!