Ok like the title post your best comebacks to any insult.
I'll start one off.

Insult: Your so dirty that when your in the bathtub the water jumps out!

Comeback: Atleast I can fit in mine.

Haha the next one I Lol'd at. My freind Morgan is quite funny, but there was a rumour going around about him so this was his comeback.

Insult: Morgan is it true your Gay?

Comeback: Haha, Yeah I don't say your Mum I say your Dad!

At the factory I've got to have some kind of a comeback or insult ready at all times. My boss at work once asked me, "Why are you so damn ugly?"

I responded, "Because I work with YOU."

A maintenance guy would also ask people at the plant, "have you ever sucked a dick you didn't like?"

When he got to me with this question, I told him, "I don't know. I've only been able to suck my own."

This kid said "This pizza frozen."

Comeback: "Your frozen!"

I laughed the most at this one.

This is my comeback to everything. Because it always works.

This is actually the best because it works in ANY circumstance.

For all of the other ones, you have to wait for somebody to say something specific and then you can respond. Which never ever, ever, ever happens.

You never happen.

Zing!

I love Mike Hobowitz.

So does your mom!

Asshole.

What's this lost turtle doing here?

YOUR MOM!

I don't make monkeys. I just train 'em!

"You're a wanker"
"I KNOW YOU ARE BUT WHAT AM I"