99% of the people on Earth have a higher than average number of legs.

And a below-average number of heads.

No flaw with math/stats here, that can actually happen. I think you're confusing average/mean with median (50-percentile).

PS: I'm not sure where he's getting his numbers though

I'm 99% sure that was tongue in cheek.

I think that it would have been even funnier to say that 99% of developers and 99% of drivers are better than the median, but I only figured this thanks to your parent's comment.

Depends which average it refers to any of the means, or the media, or the mode can be “average” (most typically, though, it means the arithmetic mean), and it's only impossible in terms of the median.

Exactly. Anything where you have a main clump with a long tail will show this pattern--most samples will be better than the mean.

You've never been on a project that was 80% done and 80% to go?

And after the second 80% is finished, then you only have 80% left.

Not native speaker here, but I think, he just meant that, most programmers and drivers thinks they are better in respective things then, they really are.

It is just like letting programmer build a house. It is just a really bad idea.