Because I said so!

We had a lot of kids in our family (5 boys, 3 girls). Mom was the sheriff, referee, etc. Whenever we got into fights she had a policy of "if you're in the vicinity, you're guilty".

One time I fiercely challenged that ruling (as I had nothing to do with it).
To which she replied "That's for the one you got away with".
Great answer, if you ask me. Left me dumb-founded!

Mine was "Keep crying like that and I'll give you a reason to cry"...

The boy next door’s mom threatened to “rip his arms off and throw them down the stairs” if he didn’t stop doing some obnoxious thing. For some reason, her threats failed to get results. I can’t fathom why...

I'll tell dad to give you something to cry about.

I like the Welsh one "All right then. Go and play your silly rugby games. But if you break your leg don't come running home to me."