Not a teen, but when I would have been 10 or so we lived out in the country, with a big eucalyptus tree in the back yard. I used to climb it a lot, and was real into building things like platforms and little (shoddy) tree houses. We also had a great trampoline, which I often used to get down out of the tree.
You might be able to see where this is going.
One day, I was up in the tree building a little ladder with the trampoline below me. I went to get down, dropped my hammer to the trampoline, and immediately followed it.
Time slowed, i witnessed it all happening in slow motion as I was thought “oh fuck, that was dumb” as the hammer hit the trampoline, i landed, and the hammer flew in a perfect arc and hit me in the forehead with the head of the hammer.
I stood there, stunned still for a second, and then immediately went “oh god, that could have been so much worse”. Thankfully I was completely fine!
A few years ago I was playing a gig in an adjoining town and after, everyone (we’d all had more than a few) piled into a car to drive back home. I just assumed the driver was all good - it wasn’t until a few hours later I realised he was pissed out of his mind and had a moment of “oh thank god we made it home”