When I have a conversation with a fellow programmer — and they know that I'm a programmer too — the tone of the conversation is adjusted to exclude explanations of commonly understood concepts.
They assume I know about variables, functions, objects, caching, blocks (or closures), loops, and flurry of other programming concepts. I do know about these concepts, at least I think I do. There's a good chance I would be challenged if I had to explain each and everyone of these concepts succinctly and clearly to someone with no prior knowledge.
Knowing how to use stuff is easy, knowing how stuff works and how to explain it to someone else is much, much harder. Regardless, as a caucasian male programmer, I benefit from the assumption that I must know about this stuff. No explaining necessary1.
Have you seen a group of programmers talk to a woman who happens to share their occupation recently? If not I suggest you crank up your awareness. Solely due to gender, many programmers will disqualify female programmers from the assumptions I benefit from. Suddenly it becomes "only fair" to ask someone you just met whether they "know how blocks work, right?".
It's really fucked up because it's utterly insidious. What's really happening there is that dudes have a positive bias towards other dudes. They're overcompensating. Although I can't deny that there must be many cases of blatant sexism and superiority complex leveled against women, what I believe to be happening is that when talking to fellow female programmers, men are indeed being as fair as they can be. They don't make any assumptions. But making assumptions that other guys "know their stuff" is almost second nature.
I'll admit that I'm simplifying. In many cases (I hope female programmers can testify to this themselves, it's not really my place to speak for them) these "fair" conversations devoid of any assumptions are laden with blatant condescension and other unsubtle cues. These act like rocket boosters to propel women into a place where they're made to feel like outsiders, like they don't belong here.
It's your responsibility as a professional to call out this bullshit as it happens. If a co-worker suddenly changes their tone when talking to someone of the opposite gender or from a different ethnic background as them. If what used to be a conversation seems to almost imperceptibly shift towards a lecture.2 It's very difficult for someone who's being put down to call out the person putting them down. Often the offense seems too small to warrant a remark.
Sadly these "little things" — as Anthony Colangelo described them in a recent episode of The Multilogue — do a lot of damage. They're not as obviously reprehensible as sexual harassment. It's far too common for people submitted these "little things" to dismiss them and keep their anger to themselves because there are worse problems to be dealt with. The "little things" quickly add up. It's past time we crush them down before they turn into big things. A single woman leaving the industry because she was made to feel constantly out of place is a tragedy for our industry, and our society.