I was working in my office this morning when I heard students walking down the hall. The next thing I knew, one of those students were standing in the middle of my office, while the other hung out in the doorway. This student -- one of my advisees -- had walked in without knocking. Without. Knocking. Or even pausing in the doorway.
The shock of it kept me from saying anything about it -- I answered the question and they went on their way.
I have a vague memory of someone doing that during advising week. Now that I know who it is, he will be getting a lesson in etiquette the next time I see him.