“Such threats are terrorism.”
No, threats are not terrorism. For that matter, terrorism rarely involves a warning.
If someone “threatens” to beat the crap out of you, just try to use that as a defense in taking him out first. You have to have to have reason to believe that the action is imminent, and that the person has he intent and the ability to carry it out.
I would personally have to show proof of such intent in order to claim I acted in self-defense. But I'm talking about the law prosecuting these nutjobs. Two different things.