Random insults - put ‘em in your memory ‘til you need ‘em:

I don’t know what makes you so dumb, but it really works.

If you spoke your mind, you’d be speechless.

If you were any smarter, I could teach you to fetch.

Brains aren’t everything; in fact, in your case, they’re nothing.

Most people live and learn. You just live.

The good news is you look like you should be respected. The bad news is you’re not.