Comment by Millennium

I'd argue that this is a matter of wisdom, not intelligence per se. Lots of smart people think others are stupid, especially when they're young. Most smart people grow out of this over time, as they gain experience. Some don't, but that's not because they get stupider. Sometimes it's due to lack of real-world experience. Other times it's inappropriate devotion to certain fictional tropes that people always seem to forget are usually villain-coded: the heroic smart guy sometimes gets frustrated but rarely complains about the intelligence of their comrades, but the villainous smart guy complains about it all the time.