Who opens the door for whom? Even if your mom told you, and you actually paid attention, the old rules are evolving.
The Standard Door
Man and woman: Traditionally, the man would open the door for the woman, and that's still fine to do, but no longer widely expected. Today, the one who arrives at the door first opens it and holds it open for the other person regardless of gender.
Man and man: Again, the person who arrives first opens the door and holds it, unless one of the men happens to be elderly or his arms are full with packages.
Woman and woman: Same as man-man.
Man who insists on opening the door for a woman: The woman may think the courtesy is dated, but it's still a courtesy. She should say, "Thank you."
Elderly person and younger adult: The more capable person opens the door.
Boss and employee: Rank does apply here. Junior executives open doors for senior executives. If your boss happens to reach for the door ahead of you, be gracious, don't fight over who gets to open door and remember to say, "Thank you."
The Revolving Door
Man and woman: Traditionally, a man would let the woman enter a moving door first, enter the section behind her, and push to keep the door moving. If the revolving door wasn't moving, he would enter first and push. Today, whoever arrives first enters first and pushes. If a door is heavy, the man may want to go first and push for the woman. But it's fine for women to go first.
Man and man: Whoever arrives first goes first. If you arrive together, the man who is younger would let the elder man go first, unless the elder man needed assistance with the door.
Woman and woman: Whoever arrives first goes first. If one of the women is elderly and needs assistance, the younger woman goes first to push the door.
Adult and child: The adult goes first.
employee: The higher ranking person enters first.
The question of male courtesy when approaching a revolving door has been addressed by Mary Killen in her 'Dear Mary' advice column in the Spectator magazine.
A reader wrote asking whether when a gentleman and a lady approach a revolving door the gentleman should enter first (so that he could do the pushing) or whether he should hang back (the traditional ladies' first etiquette). Mary Killen, as always, had an effective answer.
She advised that the man should enter first, so that he could do the pushing, but that he should do one further revolution in the door, so that he would, as a true gentleman, exit the revolving door behind the lady.