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Guys, let the ladies go first. Whether chivalrous or not, whether you are a feminist or not, just do it. This is a great way for a person to be courteous to the other and this one just happens to be gender related (which is handy so that if a guy and a girl come to a door, we know which one can go first without saying a word) :)
Example: I was coming down the elevator in my office building in downtown Seattle and I happened to be the only girl in the elevator with 5 guys. The elevator got to the lobby floor and all the guys turned to look at me because they were waiting to get out. :) I had to smile to myself and went to lunch with an extra skip in my step because it is always nice to experience another human being being courteous to the other, not to mention a person of the opposite gender, and further not to mention a whole elevator full of the opposite gender. :)