if someone behaves as if they own the place, they behave in an unpleasantly confident way.
He walked into the office on his first day as if he owned the place.
as if (one) owns the place
In a supremely confident way. The phrase sometimes indicates that the speaker is annoyed by such confidence. Ugh, the boss's son always walks through the office as if he owns the place.I want you to walk into that interview as if you own the place—no false modesty.
as if you own the place
in an overbearing or self-important manner. informal