What's something you did as a naive child that went horribly, horribly wrong? I'll start.

When I was 8 or 9, I was on the swing sets and the middle schooler boy next to me swung high up and jumped off. I thought it was so cool as I'd never seen anybody do that before, and tried the same because I wanted to impress him. Keep in mind two things:

1. I was a tiny child and to get on the swing, I had to do an awkward running jump to launch myself there. My feet didn't touch the ground.
2. This was back when all the swing set chains were not covered in rubber.

So I swung up as high as I could (not very high in retrospect) and leaped off. In my excitement I failed to notice that my cord necklace had caught onto the chains of the swing. The force of my brief flight against this jerked my entire body backwards, and I was hanging by the swing set, unable to free myself and unable to breathe. Luckily the cord wasn't THAT strong, and within a 10 seconds it snapped and I fell to the ground, crying.

The kids who were there (including the middle schooler) all saw this and one or two needed counseling from the shock. To this day I have a burn scar across my neck (I scar easily).