The most effective comeback to an insult is silence.

Sure, I'd love to help you out...now, which way did you come in?

If you took an IQ test, the results would be negative.

Sure, I've seen people like you before - but I had to pay an admission.

And I thought I had problems? Look at your face!

Your village just called. They're missing an idiot.

I'm sorry, I'm a little busy. Can i ignore you later?

I'd love to ask how old you are, but unfortunately I know you can't count that high.

Calling you an idiot would be an insult to all the stupid people.