What is the biggest insult you can come up with that doesn't involve foul language?

Source.

You have the common sense of a turkey.

Say anything nice and then follow it up with..."ON OPPOSITE DAY!"

Booooo!!!

@WalkSoftly: You love it. So shut it!

You're UGLY, & you have UGLY feet. :P

I don't want to talk to you no more, you empty-headed animal food trough wiper! I fart in your general direction! Your mother was a hamster and your father smelt of elderberries!
such a classic insult

May the fleas of a thousand camels infest your crotch and your arms be too short to scratch the itch.

Best I ever heard. A woman in her 20's eas being hit on, to the point if harassment, by a man old enough to be her father.. No, matter what he said, she didn't laugh. And refused to do"the fake giggle" Finally as serious as could be, she said..

" You are as funny as the clothes you wear

You have the IQ of a week old pile of bovine fecal matter. You are as interesting as watching paint dry. Where did you buy your clothes, the city dump? You know, s bulldog face is cute on a bulldog.... On you, not so much. Have you ever thought of riding the world of your stupidity? Well, you were almost attractive until you opened your mouth.