Eww. Well, it would depend to begin with on whether the individual doing the threatening knew where you were physically. If not, then it's bascially a non-starter (if a nasty one), isn't it?
If the individual in question DOES know where you are, then you would maybe want to contact law enforcement for your locality. If the poster who made the threat is across a state line (this presumes you and heesh are in the US), you might be referred to the FBI.
Or your local cops might simply shrug and say you've no proof it's a serious threat, and that by promulgating inflammatory content online, you may just have to deal with/ignore the fallout (which is pretty much what happens around here - not that anyone's actually been physically threatened far as I know).
I would think your reaction would depend on how seriously YOU take the saber-rattling.
No matter what you think, prank, joke or for real you should without a doubt contact your local police office. Even if you think of it as a someone playing a pretty sick prank it could very well be interprited by someone else in a totay different way. By contacting the police they may actualy be able to do something about it.
Same thoughts as Mack. Also, if your whois information is open, it means that this person 'could' make good on their threat if determined enough. No matter what, no one has the right to threaten you. They can call you every name in the book, but a threat crosses the line.
You have no idea about this person's mental state and you owe it to yourself to take your safety seriously. Even though it was probably hot air, you never know when you're dealing with a bag of hot air or a nutcase.
Even bags of hot air are capable of exploding and burning you badly. I agree with the rest: let the cops know. They probably won't be able to "do" anything about it, but you never know. If this is a pattern of behavior for this individual, there could be an authority out there compiling data to take care of it.
Do I watch Law and Order too much? Yes. Does that mean you shouldn't tell the cops? No.