I wish they would just start silently deleting his posts. No discussion, just gone, and kill the whole thread if he started it. This would require someone's time to monitor the forum carefully for a while, but eventually he'll give up because he's not getting any feedback for his trouble.
My two-year-old yells and throws objects if she's cranky and doesn't think we're paying enough attention. If we just act like it isn't happening, it ends pretty quickly and she's back to normal. I just have to make sure to wait until she's engaged with something else before I go back to clean up the mess...