Come on admit it, you thought I was going to tell a knock knock joke! Now that I have your attention, do you knock if the door is closed and you need to get into a room or a restroom? I always knock if the door is closed. When I go to the mall and there is a single restroom, I always knock on the door because I hate to walk and see someone sitting on the toilet. I always knock before I enter a room in the house because I would hate to walk in when someone is changing clothes.