Way back when, Charles White, USC tailback, was reported to be 2% body fat, I have no idea if the tests are more accurate now, but that always blew my mind, even as a youth. Pun not intended, as he developed a cocaine habit as a pro.
I remember that, and I remember it being mentioned during a game and the announcer commenting that he (White) would have a tough time staying afloat in water. It elicited a racial joke by non other than OJ Simpson, who was announcing the game as well.