Two things that don't happen to me all the time, but happen often enough to annoy:
1) At work, people observing that I'm a "woman driver." Which I guess means they have some doubt that I have the physical strength to operate a steering wheel and the mechanical aptitude to know that pushing down on the gas means go faster. Or maybe just that I'll be distracted by my nails or my period at a critical moment.
Ugh, I'm not Twisty, I know they aren't literally thinking any of these things, they're usually just kinda bemused by the novelty and joke factor of a woman behind the wheel. Like if you saw a dog driving. You don't think ill of the dog, you just have to comment.
2) People online discovering that I'm a girl, knowing nothing else about me, and immediately approaching me for hot cybersex. Really? Not that I'm always against hot cybersex, but it takes something more than the amazing discovery that we have different genders. Do you do this at the supermarket?
I'm still not Twisty, but it bothers me tremendously when I run into people talking as if "woman" was a synonym for "sexy person." That the presence of girls was both unusual and sexual, all in itself. Like people amused by "woman drivers," these people aren't the majority and they don't dominate society, but god they're obnoxious chucklefucks.
In both cases the weird common factor is people acting like women are way, way less than 50% of the population. I suppose it was true on the roads in the 1950s and the Internet in the early 90s, but times they have a-changed. At this point, there's no excuse for not getting with the program.