Politically correct ways of saying someone's stupid:

1) A few clowns short of a circus.  
2) A few fries short of a happy meal.  
3) The wheel's spinning, but the hamster's dead.  
4) All foam, no beer.  
5) The butter has slipped off his pancake.  
6) The cheese slid off his cracker.  
7) Body by Fisher, brains by Mattel.  
8) Warning: Objects in mirror are dumber than they appear.  
9) Couldn't pour water out of a boot with instructions on the heel.  
10) He fell out of the stupid tree and hit every branch on the way down.