This rule applies equally to men and women, and should ALWAYS be applied.
When you are riding in a car with either your boyfriend or girlfriend, there is no need for you to call shotgun. This is because you are expected to get this seat on every ride, regardless of you having to say shotgun. Also, if you are getting picked up, it is expected whoever is in shotgun to relinquish the seat to you.
This is the way these things work. I notice it wasn’t posted on the shotgun rules website, but this is important to remember.