Well, I'm quite certain of the function of human hair, especially that of males.

To protect against superficial injuries.


I skate quite often and sometimes I fall. That's when I get an entire patch of leg hair rubbed off, leaving me with slight abrasion that would heal overnight. Without the hair I don't think it would be quite the same.

The reason why helmets (bikers) are smooth - lest you fall, you will just roll and slide instead of landing just once and with a major concussion). So I'm guessing leg hair somewhat reduces friction and helps you to bounce off surfaces instead of you digging into it. Just run your fingers down your skin and then your leg hair (or head). The difference is extremely obvious.