1) About as sharp as a marble.
2) A few clowns short of a circus.
3) Not the brightest bulb on the Christmas Tree.
4) A few fries short of a Happy Meal.
5) The wheel's spinning, but the hamster's dead.
6) Has an IQ of 2, and it takes 3 to grunt.
7) He only has one oar in the water.
8) A few beers short of a six-pack.
9) All foam, no beer.
10) A few peas short of a casserole.
11) Doesn't have all her cornflakes in one box.
12) Receiver is off the hook.
13) His antenna doesn't pick up all the channels.
14) A few feathers short of a whole duck.
15) 24 cents short of a quarter.
16) The cheese slid off her cracker.
17) Body by Fisher, brains by Mattel.
18) Couldn't pour water out of a boot with instructions on the heel.
19) He fell out of the Stupid tree and hit every branch on the way down.
20) An intellect rivaled only by garden tools.
21) As smart as bait.
22) Chimney's clogged.
23) Doesn't have all his dogs on one leash.
24) Elevator doesn't go all the way to the top floor.
25) Forgot to pay his/her brain bill.
26) Her sewing machine's out of thread.
27) The lights are on, but nobody's home.
28) His belt doesn't go through all the loops.
29) If she had another brain, it would be lonely.
30) Missing a few buttons on his remote control.
31) No grain in the silo.
32) Proof that evolution CAN go in reverse.
33) Warning: Objects in mirror are dumber than they appear.
34) Several nuts short of a full pouch.
35) Skylight leaks a little.
36) Slinky's kinked.
37) Surfing in Nebraska.
38) Strong like bear... Smart like tractor.
39) Too much yardage between the goal posts.
40) Not the sharpest knife in the drawer.