How do you define sexes in humans?

I define it as if you born with male genitalia you are born a male and if you born with female genitalia and most of the differences in our biologies that come with being the opposite sex you are female. Is that somehow offensive?

Yes later on you might later identify as another gender but it doesn't change the reality of it even if it is polite to address people they wish to be addressed. I'm not totally educated on this but I presume even if you end up taking estrogen and getting surgery most of your components still represent your original gender... I could be wrong there because that is a guess. Under the circumstances that the guess is correct then until science has come far enough to make you more biologically the opposite gender then biologically you are still the same sex.

However despite my personal views if you identify and look like the opposite gender, I will address you that way. I just don't think what you feel you actually makes you that by definition.

Here's an example of where to me it could be a problem.. when you need to identify a person to someone else. Say a man that has very masculine traits identifies as a female then assaults you.. how are you going to describe them to the police? As female? Nope.