When I was 11 I had a scooter and decided to go down a really big hill. I picked up a lot of speed and for some reason I thought the best way to get round this bend was do a wheelie round it, came flying off and ended up on the pavement on the opposite side.
I remember going to the Botanical Gardens in Birmingham and they had a playground and one of the things you could do was try to walk across these narrow wooden beams that were a few feet off the floor. It was wet as it had been raining and I slipped, went straight down and myself and beam connected in a place Id rather we didn't. I then spun upside down and onto the floor, I was in pain.
They would get me £250 but haven't done much silly stuff in my adult life. In secondary school I did the old classic, walk across a tree trunk that goes over a river, it snapped I fell in the river ruining my brand new school shoes (They were Kickers, remember them?) my mum wasn't impressed.
I also thought you couldn't slip on a banana peel, I assumed it was just a made up thing in cartoons. I went to pretend to slip on one as a joke, because I was hilarious like that, and well I actually slipped good and proper and landed on my arse.