I just re-encountered this bit that I think every adult should know... but a surprising number either don't seem to know or don't care about: double doors for temperature control. Aka: when holding a door is the rude thing to do.
Often in the winter or yesterday at a spa with numerous saunas, including an "ice sauna", there are two doors, and inner and outer. These are to keep the cold out (or in). So you go through one, let it close (or at least mostly close) and then you open the next. But invariably there are people who open the first door - as wide as possible no less - and hold it wide open for the next person while opening the next door - as widely as possible - thus holding both doors wide open. Very often this is the same person, or group of persons, who like to stop and chat while holding the doors open, or pause to hold the doors (both) for a straggler. Its incredibly rude in its selfishness, and quite honestly just stupid behavior - do people honestly not realize there is a reason for the two sets of doors? I mean even if you've never seen it before, it seems like common sense to figure out.