Wacky insults for kids (and not so kids !)
Use your head
Use your head. It's the little things that count.
Use your head. I think you'll find it in your pocket.
It looks like you've been using your head a lot. As a bowling ball
Why don't you use you head, give it a new experience.
You must use your head a lot, I can see some of the spots where it's starting to get worn
You should use you head. There is a first time for everything.
I'd rather use your head. I prefer something that has never been used.