words or messages scrawled on the inside of public restroom's stalls, usually with deep meaning or thought. An intellectual version of Stall art or graffiti.
A: "dude, i was sittin taking a dump, and i look up and see this sharpie thing talking about how 'through graffiti two random people communicate through space and time in an instant.' it was deep."
B: "you just got metaphorically hit with a nugget of stall philosophy, man."