31 Idioms for Stupid

English has a humorous and indirect way of describing someone who acts foolishly or lacks common sense—through idioms. Rather than using harsh or insulting words like “stupid,” people often rely on colorful expressions that make the message lighter, funnier, or more sarcastic.

Whether someone is being clueless, making silly mistakes, or completely missing the point, these idioms help paint the picture in a clever way. In this article, you’ll find 31 idioms that describe foolish behavior or lack of intelligence. Each one comes with a simple meaning, real-life example, and a couple of alternative ways to say the same thing—so you can use them wisely in your conversations or writing.

Idioms for Stupid

1. Not the sharpest tool in the shed

Meaning: Someone who isn’t very intelligent or quick-thinking
In a Sentence:
– “He tried to unlock his car with a spoon—not the sharpest tool in the shed.”
– “She asked if fish need water… bless her heart.”
Other Ways to Say: Not too bright / A bit slow

2. A few fries short of a Happy Meal

Meaning: Lacking common sense or acting strangely
In a Sentence:
– “He talks to his goldfish like it answers him—a few fries short of a Happy Meal.”
– “Anyone who puts ketchup on cereal is definitely a few fries short.”
Other Ways to Say: Not all there / A little off

3. Lights are on, but nobody’s home

Meaning: Someone appears alert but isn’t really understanding or paying attention
In a Sentence:
– “He nodded the whole time, but clearly didn’t get a word—lights are on, but nobody’s home.”
– “She stared at the test like it was in alien language.”
Other Ways to Say: Zoned out / Clueless

4. Not playing with a full deck

Meaning: Lacking intelligence or acting irrationally
In a Sentence:
– “If you wear a winter coat in summer, you might not be playing with a full deck.”
– “That idea makes no sense—are you playing with a full deck?”
Other Ways to Say: Not all there / A few cards short

5. Dumber than a bag of hammers

Meaning: Extremely unintelligent
In a Sentence:
– “He glued his phone to his hand—dumber than a bag of hammers.”
– “You don’t microwave foil, genius.”
Other Ways to Say: Very stupid / No common sense

6. Elevator doesn’t go to the top floor

Meaning: Someone is not very smart or is missing some common sense
In a Sentence:
– “He thought chocolate milk comes from brown cows… the elevator doesn’t go to the top floor.”
– “Nice guy, but sometimes the elevator stops halfway up.”
Other Ways to Say: A bit slow / Missing something upstairs

7. A few screws loose

Meaning: Acting oddly, irrationally, or foolishly
In a Sentence:
– “She tried to vacuum the backyard—maybe a few screws loose.”
– “He argued with the GPS. Definitely a few screws loose.”
Other Ways to Say: Not thinking straight / Acting weird

8. Not the brightest bulb in the box

Meaning: Lacking intelligence or quick thinking
In a Sentence:
– “He got lost using Google Maps. Not the brightest bulb in the box.”
– “She tried to charge her phone in a toaster.”
Other Ways to Say: Not very smart / A bit dim

9. Can’t find his way out of a paper bag

Meaning: Incapable or clueless, especially in simple situations
In a Sentence:
– “He got confused tying his shoelaces—couldn’t find his way out of a paper bag.”
– “With directions that simple, only someone truly lost could mess it up.”
Other Ways to Say: Totally clueless / Hopeless

10. Has bats in the belfry

Meaning: Acting crazy, silly, or confused
In a Sentence:
– “She dances in the supermarket aisles—bats in the belfry.”
– “Some say he talks to plants because he thinks they talk back.”
Other Ways to Say: Nuts / Out there

11. One sandwich short of a picnic

Meaning: Slightly crazy or not thinking clearly
In a Sentence:
– “He wore sunglasses at night—one sandwich short of a picnic.”
– “She brought an empty suitcase on a trip. Something’s missing.”
Other Ways to Say: Not all there / A bit odd

12. Not firing on all cylinders

Meaning: Not performing well mentally or thinking clearly
In a Sentence:
– “He poured orange juice into his cereal. Not firing on all cylinders this morning.”
– “After staying up all night, I wasn’t firing on all cylinders.”
Other Ways to Say: Off today / Not at full power

13. Thick as a brick

Meaning: Very slow to understand or lacking intelligence
In a Sentence:
– “He didn’t get the joke even after we explained it—thick as a brick.”
– “She’s nice but thick as a brick when it comes to directions.”
Other Ways to Say: Dense / Slow to catch on

14. Missing a few marbles

Meaning: Acting a bit crazy or not all there mentally
In a Sentence:
– “He talks to his plants like they’re pets—missing a few marbles.”
– “I swear he’s missing a few marbles when he sings to his sandwich.”
Other Ways to Say: Not right in the head / A bit bonkers

15. A couple of cards short of a full deck

Meaning: Not mentally sharp or a little foolish
In a Sentence:
– “He tried to iron his shirt while wearing it… definitely a couple of cards short.”
– “Some of her ideas are creative, others just show she’s a few cards short.”
Other Ways to Say: Lacking sense / Not too smart

16. Couldn’t pour water out of a boot with instructions on the heel

Meaning: Extremely unintelligent or hopelessly clueless
In a Sentence:
– “He failed the open-book test—he couldn’t pour water out of a boot with instructions on the heel.”
– “If you need help opening a door marked ‘push,’ you might be that person.”
Other Ways to Say: Completely clueless / Utterly foolish

17. Has a mind like a sieve

Meaning: Forgets things very easily
In a Sentence:
– “He forgot his backpack, lunch, and shoes. Mind like a sieve.”
– “I told her three times, but with that sieve-brain, she still forgot.”
Other Ways to Say: Very forgetful / Nothing sticks

18. All foam, no beer

Meaning: Looks impressive but lacks real substance or intelligence
In a Sentence:
– “He talks big, but never knows what he’s doing—all foam, no beer.”
– “She uses fancy words without understanding them—classic foam, no beer.”
Other Ways to Say: All show, no brains / Empty inside

19. As bright as a burnt-out bulb

Meaning: Not smart at all
In a Sentence:
– “He submitted a blank test—bright as a burnt-out bulb.”
– “Trying to fix a computer with a hammer? That’s some dim thinking.”
Other Ways to Say: Not intelligent / Dull-minded

20. Can’t count to ten with shoes on

Meaning: Extremely unintelligent, even in simple tasks
In a Sentence:
– “He needed help spelling his own name—can’t count to ten with shoes on.”
– “When it comes to common sense, he’s totally lost.”
Other Ways to Say: Hopeless / Lacking basic ability

21. Couldn’t think his way out of a paper bag

Meaning: Lacks problem-solving ability or common sense
In a Sentence:
– “He messed up a simple task again—couldn’t think his way out of a paper bag.”
– “When it comes to fixing things, he’s totally useless.”
Other Ways to Say: Hopeless thinker / No clue

22. Has nothing between the ears

Meaning: Not intelligent; empty-headed
In a Sentence:
– “She asked if chickens have teeth—there’s nothing between the ears.”
– “He stared at the stapler like it was a spaceship.”
Other Ways to Say: Empty-headed / Airhead

23. All brawn and no brains

Meaning: Physically strong but not mentally sharp
In a Sentence:
– “Sure, he can lift 200 pounds, but don’t ask him to spell ‘lift.’”
– “He’s great at sports but all brawn and no brains.”
Other Ways to Say: Strong but not smart / Muscle over mind

24. Not the quickest bunny in the forest

Meaning: Not very intelligent or fast-thinking
In a Sentence:
– “She tried to charge her phone in a potato—definitely not the quickest bunny.”
– “He’s kind-hearted but a bit slow up there.”
Other Ways to Say: A bit slow / Not too sharp

25. His elevator stops at the mezzanine

Meaning: Doesn’t have full mental capacity or understanding
In a Sentence:
– “He confused Mars with the moon—his elevator stops at the mezzanine.”
– “Sometimes, I wonder if he’s running on half power.”
Other Ways to Say: Doesn’t get it / Missing something mentally

26. The wheel is spinning, but the hamster’s dead

Meaning: Someone looks like they’re thinking, but no real thoughts are happening
In a Sentence:
– “He stared at the math problem for 20 minutes—the wheel’s spinning, but the hamster’s dead.”
– “She looked busy, but nothing was going on upstairs.”
Other Ways to Say: Thinking without thinking / Blank upstairs

27. Couldn’t pour sand out of a boot if the instructions were on the heel

Meaning: So clueless they couldn’t follow even the simplest directions
In a Sentence:
– “He got lost using a map with a big red X—couldn’t pour sand out of a boot.”
– “Zero sense of direction or logic.”
Other Ways to Say: Hopeless / Totally confused

28. All the gear but no idea

Meaning: Has all the tools or appearance but lacks real knowledge
In a Sentence:
– “He brought all the fancy tools but didn’t know how to use them—classic all the gear, no idea.”
– “She showed up with a new laptop and couldn’t turn it on.”
Other Ways to Say: Looks smart, isn’t / All show, no know

29. Doesn’t know which way is up

Meaning: Completely confused or disoriented
In a Sentence:
– “He couldn’t tell the top from the bottom—doesn’t know which way is up.”
– “You give him simple directions and he walks in the opposite direction.”
Other Ways to Say: Confused / Totally lost

30. Brain like a pea

Meaning: Very small capacity for thinking or understanding
In a Sentence:
– “He said 2+2 is 5… brain like a pea.”
– “She asked if whales lay eggs. That’s a pea-brain moment.”
Other Ways to Say: Tiny brain / Not thinking

31. Head full of rocks

Meaning: Very unintelligent or stubbornly clueless
In a Sentence:
– “He kept arguing the Earth is flat—must have a head full of rocks.”
– “I don’t think logic ever enters that rock-filled head.”
Other Ways to Say: Dense / Completely lacking smarts

Practice Exercise

Fill in the blanks using the correct idiom from the list:

1. He bought a $200 pen and didn’t know how to use it—he’s all the __, no idea.
2. I explained the rules five times, but the __ are on and nobody’s home.
3. She argued with a microwave. I swear, she’s a few __ short of a Happy Meal.
4. He kept answering the question wrong, even with hints—thick as a __.
5. My cousin wears ski goggles in summer. I think she’s missing a few __.

Answer Key

1. gear
2. lights
3. fries
4. brick
5. marbles

Conclusion

While these idioms might sound harsh at first glance, they’re often used humorously or sarcastically to describe moments of foolishness, confusion, or just plain odd behavior. They allow us to comment on someone’s lack of sense without being too direct—and sometimes even help lighten the mood.

Just remember: idioms like these are best used playfully and not in a hurtful way. Understanding them not only helps you follow native conversations more easily but also gives you tools to express frustration or surprise with a touch of humor.