I can say that one person is male and another person is female without insulting either of them. Pointing out a difference between genders is not automatically derogatory.
No, but saying "hey, your girlfriend does this, my girlfriend does this, too! It's probably because they are both women!" is insulting if there is no reason whatsoever to believe that there really is something genetic behind the behaviour. I have seen the reverse of this too, when a friend visited and told me that I had a big LCD, just like her boyfriend, and that it was typical for males to buy large screens for their computers.
