A while ago I had a meeting with a colleague in his office. While we were talking it knocked on the door and one of our senior professors came in. He had a visitor that day and wanted to introduce him to our colleague. And obviously only to him, because he did not even greet me! Hello? We work in the same School since a bunch of years and you don't even greet me when you see me? Even if I would have been "just" a student, it would have been rude not to at least recognize my presence! And he just talked a few sentence with our colleague and walked out again. I was so baffled I couldn't even take the initiative myself. Very weird! Maybe I should walk in his office and officially introduce myself again and give him my CV or something like that.