Man, you crazy fuckers and your soccer! I routinely write hockey-related shit on the walls of friends, such as "The Leafs suck balls, and if you like them, your gay is ghey!! UR GHEY!!", and so far, no death threats.
Anyway, do you interpret this guy to be an actual threat? I bet if you showed up at his house seeking to "smooth out" the matter, he wouldn't talk so tough. Or maybe he would. I have no idea.
Regardless, document and date any correspondence you have with him.