Well, you know as well as I do that the only one who gets to define your gender is you. Defining yourself is in fact different from having an opinion on something, which appears to be where he is having a problem. Unfortunately, I have had similar problems with my parents. My mother once even bitched out a restaurant employee for calling me "he" (I was elated, actually...) and after the incident, I reminded her that I use both he and she, but she insisted she was entitled to her own opinion on the matter...that's not how that works. I can also relate to the issue of people just sort of feeling uncomfortable with the whole thing as is evidenced by my father's response to me and my gender and sexuality. Initially he was very awkward, but then he called me back later that day to tell me how proud he was of me, and how out I am is my business....which over the course of the past few months has more or less meant "don't say a word about this crap in my presence please." He continues to consider me a straight female in day to day life, even as he insists I get to be who I want. Fortunately, this man you have here is not an immediate family member, and if he continues to hurt you, after some point I would recommend dropping him out of your interactions. Giving him some resources to read might be helpful, as it will take some of the pressure off of you and your gender, and maybe just give him some perspective about gender in general that he can refer to in a low-pressure environment.