The worst one of this I had was in Orlando, where a housekeeper opened the door completely unannounced. I had the DND sign on the door and the deadbolt was set. No knock, no "housekeeeeeeping!", just unlocked the door and tried to walk right in. The privacy bar was the only thing which kept her from entering entirely. When I yelled "HEY!" she quickly closed the door and ran off, as when I opened the door I couldn't see her.

Calling down to the front desk resulted in a manager coming up immediately. He downloaded the lock log and said it'd be addressed and comp'd the room.