It started when I was a teen. I'd be writing something (notes in class more often than not) and my finger's end joint would basically get stuck. I'd have to crack it to get it to work normally again. Now I crack the end joints of my fingers allllll the time (by simply folding my fingers quickly) - sometimes it literally hurts if I don't. This is true of both hands but my left more than my right (I am right handed). My boyfriend found it creepy at first but luckily has grown to accept it.