Frankly, it is none of your business what the sex or gender of a user is. I understand that sometimes there is money to be made by collecting this information but it is also alienating and just plain irrelevant (and I think there is also money to be made in recognizing that people can be fluid.)

You can give your users an option to provide you with these details but guessing/requiring is not a good practice.

On a side note, it's interesting that the most common gender neutral title is Dr.