I fear you may take my answer to be flippant, but I assure you that it is not. My own practice is to open any door for anyone who might need the door opened. I open doors for people who are going to ride in my car; I open the door to my own office when I am about to go in and have a chat with a student; I open the door for people I have never met when I get to the door first. This plainly has nothing to dowith sexism, since I take the politness of such gestures to apply to any and all, regardless of gender or circumstance.
So it looks to me that practicing this minor bit of politesse is your answer: just be polite and open doors for anyone whenever it is feasible (without making a scene, of course!) to do so.