In the 70s, I was in door to door sales and we were taught that anytime you are at someone's door, that after knocking or ringing the bell, to move back 3 steps so that you do not appear threatening and always to wear a smile. I still follow that advice now.
Standing close in an invasion of personal space that offends or intimitates the majority of people. Just doing something dumb like that could cost you the sale or the opportunity to even present your product.
Or in this case, your life.
Very good advice. When I have occasion to be at someone's door (even if it's someone that I know), I always step back at least 7 or 8 feet from the door. I also make sure to take my hands out of my pockets.