1. His submarine has screen doors.
2. Her elevator doesn’t go the whole way to the top.
3. He’s a twinkie short of a full lunch.
4. She’s not playing with a full deck of cards.
5. He’s sharp as a marble.
6. She’s a brick shy of a full load.
7. His cheese slid off his cracker.
8. She has an intellect rivaled by garden tools.
9. He forgot to pay his brain bill.
10. Her antenna doesn’t pick up all the channels.
11. His belt doesn’t go through all the loops.
12. If she had another brain it would be lonely.
13. He’s missing a few buttons on his remote control.

And because I found so many I’m living on the wild side and doing a double Thursday Thirteen.

1. There’s no grain in his silo.
2. His skylight leaks a little.
3. Her slinky’s kinked.
4. There’s too much yardage between his goal posts.
5. He’s a few fries short of a Happy Meal.
6. She’s an experiment in Artificial Stupidity.
7. He doesn’t have all his corn flakes in one box.
8. She’s a few peas short of a casserole.
9. His wheel’s spinning, but the hamster’s dead.
10. She’s not the sharpest knife in the drawer.
11. He’s one taco short of a combination plate.
12. Her lights are on, but nobody’s home.
13. He fell out of the stupid tree and hit every branch on the way down.

Feel free to add more in the comments!

Click the top graphic to visit the Official Thursday Thirteen site.

Some more from commentors:

1. She’s not the brightest crayon in the box.
2. He’s dumber than a box of rocks.
3. They are a cup and a saucer short of a place setting.
4. He’s half a bubble off plumb.