To have a case of extreme diarrhea where the fecal matter is completely liquid. Like pissing out of your ass.
Dude don't eat that week old Taco Bell in the fridge or you'll be shissing for days.
1 more definition
To shit and piss at the same time.
Oh dude last night I had like 10 White Castle burgers with a big fucking pepsi and half hour later I was shissing like crazy while licking Concheta's vagina.