So I think there's a phenomenon here, that much like mansplaining, is so common and specific that it needs its own term. Users of this sub should be very familiar with this phenomenon. My title is the only witty way I could think to put it, but I'm fielding any better suggestions.

In short, this term isn't just plain ignorance of men about women's anatomy (I think badwomensanatomy captures that pretty well!). Rather, this term is to describe the phenomenon where a man encounters some sort of women's behavior that doesn't immediately make sense to him (either due to wrongly held misconceptions or understandable ignorance), so rather than conclude that if large swathes of the opposite gender are doing something then it probably has a logical root cause and he is either missing crucial information or misunderstanding other crucial facts, he instead concludes that there is no logical reason to do it (and women are just silly/irrational/lazy/etc.)

Examples from the typical to the slightly amusing include men who encountered sanitary pads and just assumed women were too lazy to "hold their periods"; that reddit thread where a bunch of men apparently had to be told that women don't just wrap towels around their heads for the fun of it after showers, but because long hair can be wrapped up in the towel and partially wicked dry; and a conversation I had a long time ago where a friend complained about his girlfriend "wasting money on these flimsy cylindrical bags she keeps leaving in the laundry pile" - I asked him if he knew how much she was spending on the bags and he replied something along the lines of "yeah, like 10 whole bucks!!" and then I asked him if he knew how much she was spending on the bras she puts in them so they last longer in the washing machine.