I think it is completely natural to not expect women in IT/Engineering for a variety of reasons, and how folks allow themselves to be bothered (even a little) by others having perfectly natural responses is odd to me. First, as you're aware, this is an overwhelmingly male dominated subject matter. That alone should be enough to be unbothered by assumptions regarding being a woman in IT. Secondly, lets ask why that is? I believe it is because women typically pick more personally rewarding careers partly because women are more in touch with their emotions and have better developed social intelligence compared to men. In contrast, men overwhelmingly select their career based on a combination of "What makes the most money" and "Am I able to do this task successfully", because at the end of the day men get jobs to gain resources to attract a mate. At the end of the day, thats the underlying motivation behind anything any man does really...

Take pleasure in being dismissed or treated differently, not pain. I'm a pretty successful entrepreneur having started an IT Engineering firm. I'm young, and young looking for my age at that. When I go to the bank and get in the business services line I relish in showing up unshowered, unshaved, and wearing ratty shorts and an old t-shirt just because I enjoy the assumptions people make regarding that. lol I may be weird though