I guess he props open the door a little just so people don't walk right into it.
(via redditor Among_thieves)

I don't know where this professor works, but then again, neither do his students. Apparently, this instructor hates coming into his office (you know, where students can find him and ask him questions about how to avoid failure). Seeing as he has an advanced degree, he came up with a solution: he plastered a giant poster with an image of him sitting in his chair over the door. It's the PhD. equivalent of painting eyes on your glasses so you can sleep in class.

Sources: redditor Among_thieves