When you hold your poop and then start to fart and your farts have to pass through a filter, or screen, of poop.
"Man my farts really stink right now. Oh yeah! That's because I Have to poop and my farts are passing through a screen of poop thus making them stinker. My farts are passing through my poop screen"
by Ewern December 20, 2011
Get the Poop Screenmug.