I'm going to admit something now that will get me crucified, and rightly so.
I'm a man, and I subconsciously think that women are less intelligent.
I grew up in a household where this was spouted as truth, and even though its something my conscious mind knows for a fact is not true, it's still there in the back of my mind.
I've been listening to Alaister Campbell and Rory Stewarts podcast where they interview various leaders (political, scientific, sport etc.), and they've had some spectacularly intelligent women on it. And I find myself thinking "Wow, I'm really surprised how much she's got a handle on this subject", and then catching myself and realising what a ridiculous thought that is. I even caught myself doing it on an episode where I was simultaneously getting annoyed at the two hosts being slightly misogynistic!
I do it with DP sometimes too. And while it's probably true in terms of useless general knowledge, or scientific or technical stuff, there are other areas like her mental arithmetic, or conflict resolution, where she puts me to shame.
It's an absolutely horrible bias that I've tried so hard to get rid of, but it's always going to be sat there in the back of my head because it was learnt as a kid, and I think it's too ingrained.
Weirdly, the only woman I have never done it with is DD. I've never been under any illusion that she wasn't smarter than me.
Feel free to commence kicking the shit out of me now.