Because that's what I do but it's not always done for me so I might be abnormal.
I will hold the door open for any stranger entering the building if I've passed through the entrance first and they're coming in behind me. I think it's rude to let it slam in their face. When someone does it for me, I give them a quick smile and a "thanks".
I will hold the door open for any stranger entering the building if I've passed through the entrance first and they're coming in behind me. I think it's rude to let it slam in their face. When someone does it for me, I give them a quick smile and a "thanks".

It's good manners.
I then make a very convincing scared look come on my face and I point behind them, when they turn around to look to make sure they arent about to die or something, I lock the door.
Problem solved.
Yes, I open the door for others. I'm a good person like that.
Wish you the nicest for your life. ;)