Not too long ago, a guy kept harassing a girl I was talking to. Wasn't really anything I could do without trouble because the guy was 17 so... Now, my case was a little different than yours but along the same lines, kinda. Get his number.. And post it on every fourm you a part of, etc.. And let people annoy the shit out of him. I did about a month ago and about 40+ different people were calling him. He knew his number was all across Georgia after I told him. He eventually changed his number because it went on for like 3 days. I know its Imature, but its damn funny.