proprietary air; acting like the owner
Describes someone behaving as if they own the place or are in charge, often with an air of self-importance. Used in phrases like 主人顔をする or 主人顔で振る舞う.
Even though he's a newcomer, he's already giving orders as if he owns the place.
Compound of 主人 (master, owner) and 顔 (face), literally 'master face', referring to an expression or demeanor of authority.