I work in a maternity store. I never ask people if they are pregnant. Sounds counter-intuitive, right? Wrong. Some of my customers have diseases or unfortunate shapes that make our clothes fit them better. Then again, I typically lead my conversations with "Who are we shopping for today?" (my favorite was when a customer I had seen a bunch came in with her sister, who did not look pregnant....but they were shopping for the sister, who had just found out, not the one who was due to deliver in a month). People are generally pretty accepting of saying they are or are not pregnant, as long as you don't assume and don't ask.
Of course, working in that environment has led to more than a few "When are you due"s directed at me....and I like to think that I don't look like I'm carrying anything but perhaps a big lunch.
I always get comments related to my bike not being mine, or shock that I ride (since I'm not 200lbs, covered in tatoos, and wearing fringed chaps everywhere). I have gotten used to it, now that I've been on 2 wheels for 7 years, but it still makes me laugh. Especially if I'm riding bitch on my own bike, despite looking like a "girl" bike (what with the whole girlie windscreen and all), people assume it is not mine. Fair assumption I suppose.