Ever held a dump in so long that you can feel it trying to come out of your ass, so you suck it back in using intensestrength from your sphincter, only for it to poke it's head out again? Yeah. That.
"Dude, I was walking around Blockbuster last night and had to take a dump SO bad! They didn't have a bathroom so I was prairie-doggin' while I frantically searched for Hannibal!"
to stick one's head up out of a cubicle to look at something. The term comes from prairie dogs, who burrow in the ground. In a field with prairie dogs, if there's a loud noise, typically many of them will pop their heads up out of the ground.
John trashed his monitor in a fit of rage and all the prairie dogs popped up for a look.