I quite like:
Your village called. They want their idiot back.

I often use:
If you had a brain you'd be dangerous

I've recently stopped using:
I could explain, but you wouldn't understand

In extreme situations I've used:
Please tell this to someone who *actually *gives a shit.

And when dealing with men who wont' take no for an answer...
Only when all the men, sheep *and* Monkeys die will I even CONSIDER you.

And my mother's favourite:
You don't have the intelligence god gave a lemon.