Humble brag - why am I so humble? Because everyone else is so great, too.
Everyone knows more than me about something
Here's the thing, I learned from an early age that I was "smarter" than most people. Including teachers. This became obvious when I was tested. But the other side of that is that being smarter than 95% of the people on 95% of the topics, doesn't mean what most people think it means. The inverse of that matters too.
If I meet someone new, and the average person has deep domain knowledge on 20 topics, that means they probably know more than me on at least one of them. And being smarter than 99.98% of people (where my IQ falls), even on things that I really know well, means there's still 1.5 Million people in the world that know more than me, on that stuff I think I'm an expert on. (OK. That's not exactly how the math works, and IQ isn't the same as domain knowledge, but it's a metaphor, work with me).
In the end, showing how much smarter I am than someone else is a waste of time. We all do it for puffery, at times, but the real value to me isn't in what I can teach them, but what I can learn from them. Are they one of that 1.5 Million? What are the topics that they know things I don't know?
Even if we value IQ, the truth is that hard work and research matters more -- many people that aren't as innately "smart" are far more researched and can still crush me in their areas of expertise. My IQ may be higher than Einstein or Hawking, but that doesn't mean I think I'm anywhere near as "smart" in areas that they spent a lifetime thinking about. And you don't have to go that high up the genius chain to discover the same thing.
So instead of being an arrogant douche (all the time), it's better to be inquisitive and find the things they know more on, and learn from them "the easy way" (by asking and listening).... then validating the most interesting parts with research (because as the article above discusses, trusting what you're told completely, is for rubes). I'm not an arrogant prick, most of the time, because I sincerely know that even a nitwit probably knows more than me on something, if I'm smart and humble enough to find out what that is.
Thus my inner douche only tends to come out, when someone is playing know-it-all and intellectual bullying on things they're not quite the experts they think themselves on. This goes back to those teachers that didn't like to be challenged, or bullies that would beat me up for challenging them or the teachers. If someone can't handle truths they don't like, then my reflex is to hit back. They don't have to agree with me on conclusions, but if they can't accept sub-facts because they don't fit their biases, I have to really stifle my natural tendency to torment them into growth. Which ironically, seldom leads to growth... and if I was as smart as I think I am, I could accept that these people hate mirrors and the person that would hold one up for them.