Um. Once I decided I wanted a broken arm. So I kept jumping off the otto bin. I broke nothing, not understanding that humans have a built in propensity to land like a cat from a height of about 4 feet.
I also once decided I wanted to do my 1st handstand. I never planned things in advance and just went ahead and did it. Years of ballet gave me great balance, so I'm 'standing' there on my hands for about 5 minutes too scared to drop down to stand up again.
Again, I decided once that I could do one of those backflips where you keep your feet on the ground and go over backwards til your hands touch the ground behind you. I stayed in that position for about 5 mins too scared I would get hurt if I dropped to the ground.
Once when I was about 5, I went to the newsagent with mum. She left me wandering the stationery to do something. She comes back to find me browsing through People magazine. I was apparently fascinated by the size of the boobs on the cover. Much to the amusement of the shoppers in there.
My sister once told me she could pull my toe off. Intelligent me sticks her foot out, she pulls and pulls, and it popped out of something, leaving me with a swollen big toe for a week.
I once decided while visiting my aunt that I could play with her particularly cantankerous Arab stallion. He spooked, I spooked, and took off to the neighbouring property, right into the pig enclosure. The sow spooked, about 25 kazillion piglets spooked, and I landed arse up in a very large puddle of sticky mud which they had been lounging in.
Same holiday with my aunt, I decided to see what it felt like standing on her extremely large bull ant nest on the driveway.