Edit: Fuck you downvoters. Yes, I know it's socially unacceptable to question someone's "identity". I don't care. That identity is a lie. He's a woman because he likes women's clothing just like I'm black because I love me some fried chicken.
Also, you clearly don't know anything about trans people if you think it's as simple as "dressing up like a girl".
However, that doesn't state your gender definitively. Intersexed folks exist, people who were mistakenly mis-assigned gender by their genitals exist, and you can change your legal gender, at least where I live.
Do you mean "legally a man", or "medically a man"? It is trivial to conceive of legal systems that fly in the face of what is plainly reality. The law can, and at various times and places has been, written by bigots and/or the uninformed. Who cares how it classifies things?
As for "medically a man", while it is possible to be "medically a man" or "medically a woman", for any reasonable definition of "medically", there are more than those two options.
Your comment seems to suggest that you don't realize that one's legal gender status can and often does follow one's gender identity: http://en.wikipedia.org/wiki/Legal_aspects_of_transsexualism
There's not one legal question, but many. If you live in a jurisdiction with different rights by sex-or-gender, which rights do you get? If you live in a jurisdiction with legal heterosexual marriage but illegal homosexual marriage, who may you marry? If you represent yourself as (fe)male to someone who cares, are you committing fraud? When contracts legally discriminate between genders (e.g. maybe scholarships for one gender only?), do you get to choose which gender you are for those contracts?
There're medical questions: if sex is a useful predictor of therapeutic effectiveness, what should you be telling your doctor? What should E.R. techs do? What if _gender_ is a useful predictor of therapeutic effectiveness? (Consider difficult cases like this: someone who is XY but was gender-reassigned in infancy to female (it has happened!), and raised female, and believes emself female.... which pathologies will follow male distributions, which will follow female, which will be something else?)
There're public-space social questions: which washrooms can you enter, which changerooms? (mutatis mutandis for other gendered public spaces). Can you attend girls-night-out? (Some friends-of-friends do a ladies night that includes transwomen; when I've met them, I'm inclined to think of them as dudes. How limited of me.)
And then, arguably most important, there're private social questions. We've already mostly worked out (at least in the left-leaning parts of the West) that neither sex nor gender determines who you want to have sex with, and that's probably fine (I personally think it's 100% fine!), but baby that's just the tip of the complicated iceberg. What do you do if you have an Adam's apple, and big hands, but you also have breasts, and you want to find people to discuss bra-sizing with?
tl;dr: gender and sex are complicated, and there are 2 defaults that seem to mostly-work for maybe 80%-95% of the population, and then a few more semi-defaults that work for maybe 80%-95% of those left, and then a few more defaults that work for maybe 90% of those left, and so on. And this shit matters to people, seriously. Don't be a dumbass by saying "oh it's as simple as X".
Are you this website owner ? so in the name of whom are you saying i should not hit the comment button ? who do you think you are ?
Laws are what we make them, they do not influence the nature of reality.
What I, for the life of me, cannot understand is why someone, after being informed of it, would reject the notion entirely. Where does that come from? How does someone ascribe so much importance to the concept of a gender/sex binary? Just imagine if people reacted the same to the concept of political ideologies neither republican nor democrat... I cannot fathom it, nor any reason for it.
B) People who have an emotional response to sexuality and gender are usually the ones who have repressed issues regarding their sexuality and gender identity. It's a touchy situation. On one hand I want to call you out for being a bigot on the other I feel sympathetic and wish you the best.
If you differentiate between biological sex and gender as social construct (what you call "made-up"), what is your objection to someone having a "made-up" gender identity that is different from the more common gender identity of others born with their same sex?