Okay, I’m counting to three. One…two… I mean it! I’m gonna count to three and you’ll be sorry if I get to three. One…two… What did I just say? I mean it, knock it off right now. One…two…
Legomancer, I swear that exact same monologue came out of my wife’s mouth last night (and many nights before that). I give my kids more leeway and count to 10, but at the 9 count I’m hovering over them and right as I say “10” the fur starts a-flyin’ (so I guess it’s not an idle threat). I never get to 10 anymore. 
One upshot of the count-up threat is that my daughter could count to 10 by the time she was 2 years old (yeah, she heard it that many times). Wanna know how to really piss off a 5-year-old? Threaten to start counting and then have your younger child do it for you. They enjoy the power of a parent being behind them and the older one starts doing what their told out of humiliation. I actually have my daughter supervise my son cleaning up his room. She loves it (and the room gets cleaned really fast). 
Don’t make me take off my belt (my father’s favorite from my childhood). I always wanted to keep pushing the issue just to see if his pants would fall down.
I will see you in court!!
That does it! No Christmas presents for you this year! None!
I’m gonna rip off your arm and beat you with the bloody stump!
StG
You wanna ticket to the moon? Yeah?
You wanna ticket to the moon? OK then, just keep it up.
I brought you into this world and I can take you right back out of it!
I like to say I’m gonna rip of your arm and beat you with it, and then cook it up and eat it for dinner.
Sarah Bunting (who writes the wonderful online humor column Tomato Nation) once posted a log of all the stuff she usually says to her two cats, and the list was jam-packed with idle threats. In one I particularly loved, she told one she was going to bake it into a pit and finished with “And I assure you, nutmeg BURNS.”
Crap, I meant bake it into a PIE.
This is one time when a follow-up correction was necessary (annoying as they are)
I’ll give you something to cry about!
Heehee. I was wondering how she was going to bake kitty into a pit. I thought perhaps it was a kiln, or a barbecue, or something.
Kn(wipe that grin off your face or I’ll wipe it off for you!)ckers
Hey! Don’t you sass me or you’ll really make me angry!
Actual threat from the SassyMom
I’m going to kill one of you as an example to the rest…
My mom usually says something like “I’m going to count to three, and if you don’t cut it out, you’ll be re-e-e-e-eally sorry. One… Two… two-and-a-half… two-and-three-quarters…” and usually by three-quarters my sister and I would be off and running. If we weren’t all incapacitated by laughter.
Aaah! I also threaten to take my teenagers to Judge Hatchett. Then I do my JH imitation: “You all are family. This relationship is very, very important, and if you all don’t work this out now, it is going to reflect on every aspect of your lives!”
I love Judge Hatchett.
It’ll be a three-hit fight.
Me hitting you.
You hitting the floor.
The ambulance hitting 80 mph.
[sub]I was very impressed with that one when I was about 10.[/sub]