Someone who "Pulls a Greg" is a person who spits, salivates, drools, or hocks up a fat loogie on themselves accidentally. usually while attempting to make a spit bubble, or make there spit drip all the way to the ground and suck it back up before it breaks off.
-Pulling a Greg, While Driving down the highway-
Guy one- "rolls down the window and hocks a fat loogie out the window, but the wind blows in back in his face" ahhhh f@#$ man i spit on my self!
Guy Two- Haha you pulled a Greg.
Guy One- aw man its in my eyes!!!!!!