DEAR MISS MANNERS: I work in an office with around 30 people. There are several bathrooms available to the staff, and I have used all of them at one time or another. When I am occupying any of them, I’ve noticed people never knock before trying to open the door. They will grab the handle and pull several times before they walk away. It is easy to see from the outside when the bathroom is occupied because of the type of door lock. Is it not common courtesy to knock before attempting to open a single-occupancy bathroom? I do this even at home, and definitely when entering a public restroom. GENT…