It’s like that old saying: imagine someone at the 50th percentile of intelligence. Now realize half the people in the (US/other country/world) are less intelligent than they are.
I don’t know how to “imagine someone at the 50th percentile of intelligence”. Is this some second-order joke about how 90% of people consider themselves above average intelligence, including (most likely) the person who is asked to imagine? (This percentage is completely made up.)