Those who consider themselves bright openly mock others for being less so. Even in this age of rampant concern over microaggressions and victimization, we maintain open season on the nonsmart. People who’d swerve off a cliff rather than use a pejorative for race, religion, physical appearance, or disability are all too happy to drop the s‑bomb: Indeed, degrading others for being “stupid” has become nearly automatic in all forms of disagreement.
Don't they just! At least they do on the Internet. Do they say to their pet dogs and cats "God you are so so stupid, I despise you"? We are what we are.
On the other hand I do object to people making definitive assertions which they cannot back up, and thinking you're stupid because you question their assertion, or -- heaven forbid -- even disagree with it! And this is precisely what many people tend to do on the Internet. And these people presumably tend to think of themselves as bright.
In my opinion there also seems to often be a misunderstanding about what intelligence is. Knowledge is distinct from intelligence, even though there may be an imperfect correlation. Intelligence is more like the innate capacity to understand issues, the ability to think something through rationally, to have an awareness of other possibilities and not necessarily think along pre-defined channels. I don't think one is stupid merely because they haven't heard of Kardishion (or whatever she's called). If intelligence or IQ was considered to be a reflection of how knowledgeable you are about popular culture, I would have a lower IQ than literally 99% of the population. And when I say literally, I mean literally.