When I rode my brothers old school skateboard (really, it's very oldschool) down my streets hill when it was raining, and tried to do an "ollie" (I can't do skateboard tricks to save my life) and then I flew infront of the skateboard and slid down the hill. It hurt...a lot.
Also, when I did a really sharp turn on my bike, I fell, and almost wrecked someones pick-up truck.