Think of someone of “average” intelligence. Then think half the world is dumber than that.
Okay. I’ve got you firmly fixed in my mind…
OH MY GOD!
Scary, isn’t it?
Of course, I’m obligated to ruin everyone’s fun (and probably kill this thread) by pointing out that intelligence more-or-less fits the Bell curve (“Standard Distribution”), with about 70% of the population coming in as “average.” So, only 15% are dumber than that.
But 85% of you knew that already.
Wow. Mind if I just call you Pi?
Not at all. 
Or you could just call me Approximately 3 .
<nerd mode on>
Or arccos(-1)
<nerd mode off>
Get a room.
Ooh!! Me! Me! Mistah Kottah!! Me! I’m averageish!
If memory serves, the commonly-regarded measure of Intelligence Quotient is measured on a scale of 1 (House Plant) to 180 (Wile E. Cayote, Super Genius), with what is regarded as Average Intelligence weighing in at a whopping 100, but anywhere between 90 and 120 accepted as the norm. So that plays into your “Half the people I know are stupider than me.” theory. But that’s a pretty bold generalization, in my opinion. And your statement is also somewhat provocative in that you seem to be further insinuating that those of “average intelligence” are bumbling half-wits.
I’m going out on a limb here, as I have no cites, but…
Half? Probably not. I agree with 3_14159265358979323846 about the bell curve, but my estimation of distribution is a little different. I think you end up with about a third in each segment - 1/3 roughly your intellectual equivalent- and those three segments would likely break down once again (and again). Even in the bottom third, you’d still end up with a contingent of intellectually challenged functional literates - The Forrest Gump Effect, and the Savant - a glimmer of genius shining through otherwise debilitating mental obstacles - The Rainman Effect.
Statistically, most everyone we know would fall into that middle third, with possibly a few on the House Plant side, and a few on the Super-Genius side.
However, we also need to take into account the sometimes subtle differences between intelligence and education. Third world nations, for example, undoubtedly statistically produce as many genius-level intellects as any other segment of the larger group, but there is no possible way to account for them, other than speculation standing on the shoulders of probablity. The Western notion of IQ is, indeed, stilted highly in favor of Western thought. The assimilation of ideas and thoughts, rationalization processes, and logic as seen throught the eyes of a population grounded in science and mathematics cannot possibly account for the variety of genius the world produces. It would be certainly hard to swallow the concept that a Bushman cowering before an eclipse could be your intellectual superior, but is is possible, nonetheless. The ancient Egyptians couldn’t build a Nuclear Submarine, but niether could I for that matter. But (and this is important) we still can’t definitively say how they built those damn Pyramids. There are many examples of this type of ingenuity in history - Stonehenge, Easter Island, the Aztec Pyramids, and countless others dating back millenia. Or more recently, how Edward Leedskalnin - a Latvian with the equivalent of a fourth-grade education - managed to build Coral Castle. And what about musical prodigies?
Then again, I might just be talking out my ass.