Personally, I feel a lot of people give themselves needless worry and stress on the "do I pass" thing. If you are confident in who you are, that confidence will show on the outside too and it really can just be a simple matter of correcting someone who might get it wrong (only if you choose to correct them and in certain situations). Even if you have to still live your life as male and you're really female or vice versa, if you know who you are on the inside you can develop an inner confidence in yourself that will show on the outside.
Before everyone reiterates the safety thing, let me expand on safety myself.
I pretty much grew up in Los Angeles. Anyway, I've been all over that city over the years. I used to go to raves in abandoned buildings down on Gage. I used to eat chicken and waffles at Rosco's (and I used to live a couple miles from there and sometimes walk down there). I used to bring my camera and take photos downtown, all over Hollywood, and in parts of the L.A. river (for those of you unfamiliar with the L.A. "river" it's all concrete and in some areas covered with amazing graffiti). In all the years I lived there, I was never f**cked with except for one isolated incident in my own apartment ... and I've been female, male and in-between. I'm no where near physically imposing. I'm white and 5'3" and even in guy mode can still be taken as a female sometimes. I've had friends that lived somewhere else and moved to L.A. and every one of them has had something happen to them - cars stolen, beaten up, mugged. I've known a number of people from there that have had problems. What I attribute my record of not having any problems to is not just attitude (which does go a long way - if you walk down the street confident, you do not make yourself an "easy" target) but awareness. I have absolutely, personally witnessed some very, very sketchy ->-bleeped-<- go down. There were places where I would rather piss in a bottle in my car than get out. There were places where I'd drive through a red light in my car rather than stop. There were places where I would walk down one street that was out of the way instead of talking a more direct route. Being totally aware of your surroundings and the people in those surrounding is a very key skill to cultivate - whether you live in the big city or not. Sometimes this does mean modifying your behavior. Some people might not be "cool" with this but I can tell you it's better to be aware and avoid a situation then be subjected to something bad going down. I've even been in a few occasions where there were not easy options to just avoid it. Luckily, I'm a damn good actor when I need to be. I've been to places where I walk in, and pretty much walk right out. I've always considered myself empathetic as well. If some place just has a weird vibe, I will avoid it. This includes bars, shops, restrooms, whatever. I know not everyone has a heightened sense of what might be impending doom but just getting familiar with your surroundings, other people's body language, etc. can literally be a life saver.
Some might totally call me a cop-out or a pussy or any other names because I'm not the "out and proud" type and I'm not beneath playing the part of the opposite gender if I know it would behoove me to do so in a particular situation. But I'm all about self-preservation just as much as I am about self-expression and just being yourself. But to me, safety takes precedence.
A few years ago I went to NYC for the first time. Everyone told me, oh you have to really watch yourself there! Really, I just behaved like I did when I lived in L.A. - I was totally aware of the surroundings - even though they were unfamiliar to me - and I walked with my head up like I knew exactly where I was going with confidence (even if I didn't!). I had other "tourists" asking me for directions. I was there for a couple weeks and every night I would walk a couple blocks from the hotel (which was between China Town and SoHo) to this 24 hr market and get some snacks or water. I saw the most amazing things at 1am in NYC. Giant rats. Crazy bums. People having arguments. Just a whole bunch of random stuff. There were a few times where I rode the subway late. I caught on pretty quickly to subway etiquette though and even when there was the crazy guy who was trying to get in people's faces I managed to get through the experience unscathed. I'd totally go to NYC again in a heartbeat.
And I know that even with being aware and confident, things can still happen. But I feel like at least the odds are lower and I really do believe in the power of the mind. There's also been a number of studies having to do with criminals and victims. Criminals have come right out and said they specifically look for "easy pray" - that is the people walking with their heads down at the ground, unaware of their surroundings, people who were obviously nervous or "out of place", people fumbling for their keys ... The majority of criminals or people bent on doing others harm seem to have a sixth sense and are able to spot those easy targets. They're able to "smell fear" and things like that. If you're ever in or around a dangerous situation the worst thing you can do is appear nervous or fearful or freak out.
I hope that no one here has to deal with a dangerous situation but I hope that these few tips might help out just in your general life - to me more aware of your surroundings and situations that have the potential to be a problem.