how many ways have you messed up your body?
Oh I stopped keeping track a long time ago, but the part most messed up? I'd probably have to say my back.
Had a bad fall once off of a icy roof as I slipped while climbing down, rotated in air such that I fell flat on my back. Didn't help that rather than counter rotating with my arms I let my arms fling along in same direction adding to the momentum and right arm was left right across and under my spine as I hit the ground. After that for a good few months as I was about to fall asleep my arms and legs would twitch and fling around immediately waking me back up again. Still occasionally happens though not as bad anymore, 13 years later.
Never looked into proper form for working out, always just winged it based on instinct. So no advice to give there, sorry.
edit: Ooh, ok another good one I just remembered. Last time I drank, a new years eve I chose to walk a 2 hours on foot trek back home through the city drunk likely coming close to some form of frostbite. Ever since when it gets cold outside should I step outside shivers immediately kick in to I presume instinctively keep my body warm. I don't necessarily even feel cold, but I guess the body knows even if the nerves can't quite yet feel it.
Ah, another one, when about 3 or 4 years old I rummage through an gigantic old antique wardrobe full of random bits and bobs. Amongst there was a death cable. What's a dumb kid to do but to be curious like a cat, right? Luckily I didn't get a good grip. So still alive obviously but through out the school life whenever they'd do the health checkups I'd always be recommended to go check out a 'suspicious heart murmur' , which naturally I've always ignored and left neglected. I do sometimes feel it almost missing a beat tho.
Don't be like me, don't be neglectful. I guess that's the moral of the stories? Eh good advice either-ways.