I worked for a company that had 0 female programmers. "How curious", I thought as a fresh grad, "that while there were some women in my CS classes, there were none at the company". "Well, there are only 30-40 of us, so it must simply be a quirk of statistics."
Yeah no, the owner didn't think women could handle production systems so he only hired men. He told us this directly at lunch one day. He looks exactly how you're probably imagining he looks based on that statement. His wife made him give me a bigger bonus one year because at a company dinner, I made the mistake of sitting next to her because I didn't recognize who she was, and mentioned (over the course of dinner) that my wife and I wanted 3 kids and she was going to be a stay-at-home mother. I worked there for far too long because I was a new grad who hadn't ever left a job before.
It being so obvious at my first job was honestly a good wake-up call, because now that my generic white male illusion that it's all in the past was soundly shattered, I see it's more insidious forms. Like at my next job, how the one woman on our team was suspiciously the only one who took longer than 2 years to get promoted from [mid-level eng] to [career level / sr eng]. I don't think that one was nearly as explicit, but I no longer sit here and go "hmm how curious that the only woman is the only one who didn't fit the pattern". It's because of unconscious biases in the promotion review panels.