Hrm... let's see... about men who are handsome but lacking in the most important way
"He may be easy on the eyes, but damn, he's as dumb as a stick."

Dumb as a box of rocks (another teacher uses that one)

Not the brightest crayon in the box (art teacher)

Usually any That 70's shows lines like "Eric, you don't have bad luck son, you're just a dumbass. (I tend to say dumbass quite frequently.

Oh, and my typical line after a friend or a kid said something really really stupid, and they know they said somehting stupid ... "LEAN IN..." and they know what comes next... ME, slapping them upside the head for their stupidity, lol. Never hard, but they know, and I'll get soem who say "Come on, you know what you have to do now!"

It's fun!