Now that I think about it, when I was in high school in the 80's, kids used to put safety pins on their coats, usually on the sleeve. I am sure that someone saw some rockstar do it or something, I don't know where it started. Some kids would take the time (most likely during study hall) to line 30 or 40 up going down the entire length of the sleeve.
It wasn't before long when the rumor started that kids were putting a safety pin on their coat for every time they had sex with their boyfriend/girlfiend. It was just an urban legend but I remember what a big buzz it made around school for a while.