I dont think passing perfectly means living in fear of being found out.. surely thats passing 'not quite perfectly'?
I do see thier point though, I'm in a similar boat. Pretty much everyone I know, knows only a girl, and that gets sticky at times... when we discuss girl things... mostly childhood and feminine issues... I'm totally comfortable with the boy talk, and chaging around friends, but its the discussion of periods, the pill, examinations, things in our teens that i fall over on. I've lied a few times, creatively suggesting one thing, while not saying it... its not QUITE a lie right? Yes, its quite emotionally heavy at times, but its not something i chose, and id NEVER choose to out myself. I'm happy just being one of the girls.
Its a fine line to tread, i dont think everyone can cope with it. Perhaps I'm a fast learner, or im just naturally this way. But I manage to break the uncomfortableness down and take part without taking part...
Though my most uncomfortable was over the summer when I was working home in Ireland, i was stood outside work having a cigarette, and i had a minor stomach cramp... i hadnt eaten much that day... the boss was next to me, and she sees this, and asks 'is it your time of the month?' im like 'erm,' and she takes that for me being embarassed about my period.... and gets all hyper sympathetic.... cue 'i dont want to watch' cringe sitcom moment....