No joke.. Give him a call and tell his ass whatsup.. When he hears the sh!tty tone in your voice, he'll most likely pull his head out of his butt and call you back.. Believe me, I do collections for a living.. It also helps that I have a really intimidating voice and know how to make people to fork over the money, or the headlights in this case.. Give him a call and leave him a message, telling him you're giving him until X-date before you start to pursue him legally..
Mark