At the bank of ATMs at my bank, there is occasionally a person who holds the door open, saving after-hours visitors the agony of inserting the card they will use later anyway in a slot near the door in order to unlock it. In exchange this person is hoping for a little something on the way out.
On my way in I tend to have nothing, and on my way out I have nothing but twenties. I assume others are in a similar situation. If I were an honest and consistent person I guess I'd have to decline the open door and insist on opening it myself because I know I'm not going to trade a twenty for the service.
As it is I give the usual noncommittal hypocritical nod/headshake/mumble and go on my way.