Threatening PM?
Copy, paste, and post it here. Report it to the mods, and if it's REALLY threatening, report it to the proper authorities. Print yourself a copy for future laughs.
Otherwise, ignore him, and block him....

There was once a guy from "Canada" who got mad because I told him his "Skyward" engine wasn't a S.T., and he threatened to "come up there and know your chicklets out" Haw Haw! he obviously never made it here, and is still on the road, somewhere near the Artic circle!
I printed out the e-mail and still have it.