This happened when I was maybe three or four, and completely obsessed with swimming and being in water.
We were at the swimming pool and my mum made me get out because it was time to go home, I didn't want to, and for some reason I got this idea in my head that if I could get myself back into the water, my mum would just... give up and let me stay in the pool indefinitely?
But I knew if I jumped in on purpose I'd get into Big Trouble, so I very cleverly (I thought) figured out that if I could stage things so it looked like I'd fallen in by accident, that I wouldn't get into trouble and my mum would let me stay in the pool.
I walked to the deep end and stood facing away from the pool with my heels hanging over the edge, then "absently mindedly" stepped backwards.
And honestly plummeting straight to the bottom of the deep end wasn't a problem, since I knew that would happen and didn't mind, if only I'd known there was a grille covering the filter right below where I'd stepped in.
I don't know why I thought my mum wouldn't react to her only child suddenly plummeting into the depths of the deep end, but she sure as hell reacted to me surfacing with blood streaming down my face. As did literally every other person in the pool.
And that's the story of why the very top corner of my upper lip is missing to this day.