In my comment I used a line from The Last Starfighter. There is a scene where Xur says something about being accepted as ruler or something by some group of people, and he finishes the statement with, "...or I will darken the skies with their ashes!"
That's pretty awesome, actually. So I use it whenever I have need of a good non-specific threat and can crowbar it into place.
Another good threat I heard was from a comedian: "I'll hit you so hard your kids will be dizzy!" And on a sitcom that starred Burt Reynolds, he had a similar line: "I'll hit him so hard his parents will die."
From bash.org: "I'll hack you so bad your ancestor's house will burst into flame."
Of course, Dr. Detroit had the best: "I'm going to rip off your head and shit down your neck."
Still, it doesn't have the "awesome" factor of Xur's line. "I'm going to pound you so hard it'll cause another fricking ice age!" I like that.