You really would have to read deep into that for it to be a threat wouldn't you?
That is not a threat IMO, just someone ranting and raving. He prob forgot he even sent you the email by now....
"**** you and your piece of **** hummer, I outta shove it up your ass"
"I'm gonna find you and stick your hummer up your ass"
"your dead **** head"
those are threats.......You are reading into it waaaay to much.