What stupid injury left a long lasting impact on you?
I'll start: I tried to move a bookshelf while drunk about 6 years ago and tore a tendon in my shoulder pretty damn good. It still bothers me sometimes if I move it wrong or sleep on it wrong.
It doesn't really bother me anymore physically, but I have a scar that has acted as a reminder not to do stupid shit. When I was a teenager, we had a broken mirror outside. I thought, it's already broken, who cares if I break it more? So I smashed it with a hammer, with no gloves or anything. Sliced open my finger. It's the index finger on my dominant hand, on the back side of it, so it's very easy for me to see. Seeing that scar may have saved me from doing other dumb shit.
I have huge scar from similar thing - somehow I got too close to my friend with machette. No one knows how it happened but it remindes me to newer get close to someone with dangerous things. It is about 10 cm long on my left arm.