Our nurse at the hospital, along with the most annoying people I've ever known, says, "knock knock" out loud when she enters the room.

There's no door

Buy her a piece of wood for her birthday so she has something to knock on before entering. Put it on a necklace, and call it fashionable. Make bad knock knock jokes about her afterward until she stops. Refer to her as Woody thereafter.

@Root mastermind