Not too long ago I knocked before entering a room. It is just automatic for me. The weird thing was, I was at home and the room was our bedroom. Mike was inside. He just looked up at me as I entered and said, "Well, that's new."
This week I over-knocked yet again. I was in PACU (Post-Anesthesia Care Unit...formerly known as a recovery room) and as I was going from that unit out to the hallway, I knocked. No one answered. I'm not sure who, if anybody, saw me knocking before entering the hallway, but I burst out laughing at myself. I thought it might tickle you as well.
If I made you smile, my mission is complete.