There seem to be a few each year that are memorable - like the idiot who thought a crowded trail was the place to teach himself how to rollerblade backward.

But the guy my wife and I saw the other evening takes the cake, IMO - he was riding no-handed on his mountain bike, strumming his guitar. A full-sized dreadnaught, no less. Amazing. And a very effective demonstration of the doppler effect as he passed.