On sale at Walmart

Diarrhea.

*derived from "I am going to Walmart" as code for "I shall now use the bathroom to poo" or "I am going to the bathroom to fart away from human presence as a courtesy to the world."

Everything's on sale at Walmart, cuz the poop wouldn't stop flying outta my butt!
Damn, I popped a squat, but it was all liquid. Walmart must be having a sale.

Person 1: You were in there a while, everything okay?
Person 2: There was a sale at Walmart.