What am I missing here? "Die slow" is certainly in poor taste, but it is not a death threat nor is it a call for violence. It seems clear to me that it expresses a wish for the target to die slowly (and presumably painfully or uncomfortably) when they do end up dying. It's childish and mean spirited, but it's clearly not a threat. I'm more afraid of the chilling effect that punishing this sort of harmless speech has than I am of allowing it to continue through inaction.