You have to take a crap so bad and because it's fully brewed it's pressing upon your sphincter. The skin on your entire body breaks out into goosebumps.
"We have to pull over, man. It's been 4 hours since we left and I have to take a dump so bad that I have shitbumps! See them?"
The Goose bumps your bodey produces in the act of shitting or about to go shitting
God dammit steven i got shit bumps on my arm i might be shitting or about to go shitting.
The goosebumps that cover your entire body as you shiver and shake with the pains of severe diarrhea.
Dude: It's 95 degrees outside, why do you have goosebumps?
Dude 2: They aren't goosebumps man, it's the shit bumps. Goddamn baked beans!