Justin Bieber Pisses Himself in Colorado

Justin Bieber has already marked his territory in Colorado ... pissing his initials in the snow ... while nearby residents looked on in disbelief.

An eyewitness tells TMZ ... Bieber and his crew were driving in Snowmass, CO, Sunday when his motorcade of Escalades pulled to the side of a private road in a wealthy residential area.

We're told Bieber hopped out, surrounded by bodyguards, and proceeded to whizz in the snow.

Bieber was gone in a flash, and stunned residents went over to inspect the scene ... where they say Bieber had peed his initials "JB" in the snow (PHOTO).

Probably not the smartest move when he's having trouble with cops ... but at least it wasn't a mop bucket.