My Last, Worst Spanking
When I was a month short of my 15th birthday, I did something at my grandparents' house that was really stupid and endangered some other kids. I won't get into the whole timeline of it but basically it involved a friend of mine swinging a knife around that we'd stolen from my grandpa's basement. Word went from the other kids' parents to my grandparents, who sent me upstairs and called my mom. Mom had a class that night, so I had to wait and sweat it out upstairs for three hours until she came to fetch me.
She told me right out that I was really in for a good licking (as well as being grounded to my room for a month). She borrowed my grandpa's army belt, which she'd never done before, and asked me if I'd be able to hold still for it. I told her I didn't know and she might want to bring my grandpa up to help her (he had done this at times when I was younger and couldn't hold still). I got undressed and when my grandpa came up to the room he tried to figure out how best to proceed. Well, he told me to lie on my back and before I knew it he'd grabbed my ankles with one hand and bent my legs so far back towards my head that I could smell my feet. Then mom went to work whipping my butt with the belt, but the pain in my legs was actually worse, and I had bruises on my ankles as well as my butt for the next week. Yes, it was overkill and I could've called in a case of child abuse if I'd wanted to, but under the circumstances it was fully deserved.
I think the results of it scared mom though, because she never spanked me again, although the threat of it was there until I left home.