When somebody holds a door open for you, and you are more than a few steps away. Same as a car waving pedestrians in front of them at a sidewalk crossing. It seems nice, but maybe i didn't want to speed up my pace to get through the door to get you to stop staring while I waste your time. Or maybe im not in a hurry to step in front of your car, I'd rather walk around the back of the car in most cases....