When things happen to me involving my birth name (which is embarassingly feminine) it's made even more embarassing by the fact that I haven't used that name in a good seven years or so and it's really rare.
It happened recently when I went to a hospital that I hadn't been to since I was 2 or so, and I was still in their records. I politely explained my situation and that I'd appreciate it if they'd call me by my LEGAL name, not birth name, because there's people around (in a very closed-minded town). They flat-out refused until I provided proof of legal name change, and so I've never been back, but they recently sent me mail with my old name on it, which is infuriating. I didn't even ask for them to change the name in paperwork, just to refer to me in a proper, reasonable way.
Another incident, strangely occurred at work where everyone knows of me as a guy, and no one except I'm guessing my boss, knows the truth. I have a pretty deep voice thanks to hormone treatment, and it's been a while since anyone has questioned me.
We were changing shifts, and I work at a convenience store. The guy coming on after me, and older guy, was getting his stuff together, and I was emptying my till. A customer was standing there waiting, and asked what was going on, and the guy says "I'll be able to help you, as soon as she gets out of her till"
The customer was obviously confused, and I was obviously mortified.
I wasn't sure if I should say something, or if it would raise more questions NOT to say something, but I didn't.
Needless to say, it was a confidence killer.