- You live in a building and you see other people who live in the building with their hands full of groceries. They are about five feet away from the door as you exit the building. If you allowed the door to close, they would have to put down their groceries, fish around for keys and maneuver through the door while holding it themselves. If you leave them to do this, you are one oblivious motherfucker.
- You are exiting a building with a prox card (perhaps a university building) and you see someone walking up to the building. You would not even have to hold the door open if you only opened the door all the way. If you instead slide through the smallest crack of door that remains open from when the previous person opened the door*, letting the door shut right as the poor next person walks up to it, you are either extremely rude or completely socially unaware.
*Rather than go through the risky acrobatics, isn't it easier just to open the door?