When someone is so high on adrenaline, that they let out a little bit of piss.
Similar to when one sneezes with a full bladder and lets out a little.
May vary from a dribble to a full on wet your pants depending on bladder and adrenaline levels/conditions.
person 1: "daaamn dude i totally had an ADRENALINE PISS when we went over those train tracks doing 70 and were airborne for like 3 seconds, not gonna lie!!!"
person 2: "OMG same here dude"