When in doubt, it is always most proper to hold the door for the person behind you. The distance, however, has been a matter of some debate. Some authorities hold it best to judge whether you can see them coming, but if you can clearly hear their footsteps coming around the corner, it is often better to wait for them just in case. Keep in mind that once you have held the door for one stranger, it is your responsibility to hold the post until there is a lull in doorway traffic (see Jaywalking guidelines).
If you hold the door for someone you assume is a stranger coming around the corner, and
it turns out they are an acquaintance, there are a few special points of etiquette.
Your crush: open the door a little wider and pretend you are only wasting a little bit of your time holding open doors, because it’s them.
Your ex: shut the door and leave (you just like lounging on open doors, obviously, and now you have a class to get to).
Your professor: assume a blank face and feign a lack of recognition.
The TA who gave you a bad grade last quarter: blockade the doorway and take a nap so they can’t get through.
Your friend: shut the door and proceed to walk into the building as if from the other
direction so that they will open the door for you and thus prove their friendship.
Your significant other: depending on your current feelings, any action applicable.
Often you may find yourself walking towards a door in the company of someone else. It is always a gentleman’s responsibility to hold open doors for ladies. However, women at the University of Chicago have read Judith Butler and they should thus never allow anyone to hold open doors for them. In large groups, as soon as a door is in sight, all members of the party just race to see who can open the door first. If any member of the party has their hands full, it is doubly their responsibility to hold the door for the others in order to prove their selflessness and devotion. If, as a result, people trip, fall, and dogpile, the person most affected must apologize profusely for failing to hold the door themselves.