A320
Flight Crew Last 90 Days 244; Flight Crew Total 19675; Flight Crew Type 2300
Physiological - Other
Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Security
General None Reported / Taken
Human Factors
Upon setting the parking brake and shutting down the right engine; the Captain announced he had to go back and use the restroom.  Upon returning to his seat; he said that his understanding was that since the aircraft was effectively disabled with an engine shutdown; he could do so without calling the Flight Attendant and setting up the barrier.  We then taxied to the gate without further incident.
Air carrier First Officer reports the Captain using the restroom facilities while waiting for a gate with one engine shut down and the parking brake set; without summoning a Flight Attendant.