I am looking for a word/phrase that means "being temporarily stupid/silly" and fits in these situations.

Situation A Some guy solves a math problem using a very complex method, and some other person shows him a very simple solution. The guys then says: "Oh! Right! I just ___(requested word/phrase)."

Situation B Someone is calling a friend using his/her cellphone, and suddenly yells "Where's my phone? I can't find my phone!" And we can say this person is ___(requested word/phrase)

Situation C Husband gets ripped off but doesn't know about it, and wife shouts: "What were you thinking? Did you ___(requested word/phrase)? How could you fall for that crap?"

Situation D Someone wants to say something but immediately forgets, and he/she mocks himself/herself: "Oh I just ___(requested word/phrase)"

To those who know about Chinese, I am looking for a translation of 脑袋短路. I've asked this on our Chinese site, but the answers there had some controversies. One option is "blank out", which works for D but not the other three. Other options include "brain glitch", "brain fart". But google search tells me these refer to mental illnesses rather than just being temporarily stupid.

Thanks for all the answers that are already here! It seems that there are more ways to express this than I have thought. So if you have a new idea please feel free to add an answer or comment even though I've already accepted one. Due to the possibility that a single word may not work for all the four situations, a specific answer to only one of them is also welcome.

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    This is how to ask a "what is the word for..." question. Clear context, a justification for why the word should exist, evidence of prior research. Good job.
    – James K
    Commented Aug 19, 2019 at 6:36

8 Answers 8


"Blank out", "brain glitch", and "brain fart" are not mental illnesses. They are all legitimate, albeit possibly crude, vernacular for temporary stupidity.

There are others such as "senior moment". This is a facetious reference to the kind of absent-minded dementia occurring in the elderly.

I forgot my phone when I left the house this morning. I must have been having a senior moment.

Interestingly enough, Google translates 脑袋短路 as "short circuit". You can use the same metaphor in English:

My brain must have short-circuited

My brain was on the fritz.

My brain blew a fuse.

and so on.

  • For situation A, see the story about John von Neumann at mathworld.wolfram.com/TwoTrainsPuzzle.html ;-) Commented Aug 19, 2019 at 6:21
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    Although "senior moment" alludes to dementia, I think it's often used facetiously by people who don't necessarily believe they're demented. It's a convenient excuse for ordinary absent-mindedness.
    – Barmar
    Commented Aug 19, 2019 at 15:08
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    "Brain fart" was the first thing I thought of, but I don't think it really fits in Situation C.
    – Daniel
    Commented Aug 19, 2019 at 16:42
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    In my experience "blew a fuse" is more of an anger problem than a mental problem. As a native English speaker from the MidWest, I wouldn't recognize this as a temporary cognitive issue. I'd hesitate for an ELL to use this one, as it has a possible negative side confusing the issue and the ELL when confronted on it. Commented Aug 19, 2019 at 19:44
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    To be clear, "brain fart" is pretty crude. You could use it among friends but never in a professional context. Commented Aug 20, 2019 at 2:56

Discombobulated is a nice word that implies temporary confusion.

  • +1 Agreed. It is quite literally a "nice" word, as it implies momentary confusion rather than some kind of innate inability. :)
    – Andrew
    Commented Aug 19, 2019 at 23:28

'I just lost my train of thought' can be described in the case that I just forgot what I was talking or thinking previously, it might suit some of your situations.

Merriam-Webster's definition of train of thought even includes a sample usage that mirrors what you are asking about:

train of thought (noun phrase) a series of thoughts or ideas that someone is having
You interrupted my train of thought.
I lost my train of thought when you interrupted me.

  • Or "My train of thought jumped the tracks" :)
    – Andrew
    Commented Aug 19, 2019 at 23:26

I quite often use the phrase 'slipped a cog', implying my mental machinery momentarily stuttered. I think I picked the phrase up from a grandparent several decades back.

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    +1 I was thinking "threw a gear" -- but whether you say "gear" or "cog" seems like another of those things based on location.
    – Andrew
    Commented Aug 19, 2019 at 23:27

I very much agree with Andrew,

But then: Situation A is a little bit exceptional as, compared to the other situations, it's a kind of "overthinking" issue. I would generally say that in English it's probably a separate word (literally overthinking)

For Situations B, C, and D you could say:

British English "Lapse": a slip; error

to have a blackout (blackout refers to memory issues, in B it would be I forgot where I put my cellphone, it can also refer to not thinking or forgetting for C & D)

to have a dropout

the mind went blank for a moment (although it often refers to "what was I gonna say" it can be used also in C and modified in B)

my mind was on standby (B,C,D)

my neurons were on holidays (B,C,D) or as the pixies put it where is my mind (and the analogues where was your mind when...)

Nowadays a sexist answer: to have a blonde moment (it's referring to blonde jokes)

Lastly, a more modern version: What was [I/he/she] smoking? (a humorous reference to drugs)

  • 6
    Are you a native speaker of English? I've never heard expressions like have a dropout or neurons on holidays. Lapsus and lapse aren't exclusively BrE. Have a blackout doesn't really work here at all, and mind on standby also isn't very suitable (okay, maybe for the last one).
    – user3395
    Commented Aug 19, 2019 at 14:30
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    @userr2684291 - I agree with you; many of these are either nonstandard expressions or not often used in the OP's context (although I must say, I like the originality of "neurons on holiday").
    – J.R.
    Commented Aug 19, 2019 at 14:43
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    You can be creative in English, if the thing works. Drop out does not work. Drop out implies a line of objects or a place from which something or someone falls or is removed. Therefore, a brain cannot drop out. Neurons on vacation is French and, of course, it can be understood. Blackout as with electricity could possibly work.
    – Lambie
    Commented Aug 19, 2019 at 15:12
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    I also work in IT, but 'drop out' evokes 'drop out of school' quite strongly -- something that is often considered quite permanent. 'My brain dropped some packets' would be much more clear, at least in my circles, but that requires some familiarity with computer networking.
    – Phlarx
    Commented Aug 19, 2019 at 15:31
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    I think I'd disagree that Blonde moment is sexist. I've heard it a lot and it is definitely slang but both sexes can be blond(e) and have a blond(e) moment.
    – mjaggard
    Commented Aug 19, 2019 at 15:52

For situation A, I've used the excuse "I guess I can't do math today."

Situation B is definitely an example of a "senior moment".

While situation D is where "brain fart" could easily be used.

The instance of Situation C is more difficult. I can't think of a good word of phrase for that one. About the only thing I can think of is "lose your mind". "Losing your mind" can mean getting mad or having a disease (like Alzheimer's or dementia), so be careful using this one. Most people will react to it in a negative way, as it's much more insulting than most other examples suggested to your Question. This can also be made much more derogatory by adding an expletive right before "mind".

A phrase the other good answers haven't mentioned is "brain fog" or "I'm in a fog".
Blaming this kinds of behavior on "low blood sugar" is somewhat common, but can also mean that you are feeling generally sluggish.
I've also heard and used "too many things on the brain", meaning you can't concentrate on any one thing right now. This would be similar to "mom brain" that TinMan mentioned in a comment.

If you totally lose focus on something, you can say "I'm sorry, I don't know where I just went". This would be appropriate if you are essentially day dreaming or just space off while people are talking to you, with you being silent when they expect an answer.
Also, saying that you "temporarily faded out", as in lost focus on a single task, can be used.


"Silly me!" and variants like "I'm (so) dumb" are often used in the first person. Although I think a simple "oops" or "whoops" are even more common.

As an actual name for the event, "having a brain fart" is the most common one I encounter. That said, I think generally people just describe what happened without giving it such a label.

"What possessed you??" would be quite appropriate in situation C. This alludes to a spirit taking control of your mind for a moment. It is used for more serious mistakes or for behaviour that is hard to understand (unlike B or D which happen to everybody.) "What were you thinking?" is similar.

Although it doesn't really work in the sentences you provided, a useful phrase is "goofing up", which is a lot softer than "screwing up". It is usually taken as making silly mistakes that are reasonably harmless. It is closest to situation B (assuming we are talking about a small amount of money) because the others don't really have a negative outcome.


Situation D Someone wants to say something but immediately forgets, and he/she mocks himself/herself: "Oh I just ___(requested word/phrase)"

In this situation one might say:

I have a memory/mind like a sieve. (= I have an extremely bad memory)

Perhaps, something is on the tip of your tongue (you know it (e.g. a name) but you can't remember it at the time you are speaking). Then you can also say:

Oh, it just slipped my memory/mind. (= I forgot it)

The idioms above are about being forgetful rather than stupid or silly. But they are appropriate in situation D because forgetfulness seems to be the main problem there. It causes the mocking.

Situation C is different. The man gets ripped off and his wife might shout:

What were you thinking? Do you have a screw loose? How could you fall for that crap?

If you say that someone has a screw loose, you mean that they behave in a strange way and seem slightly mentally ill.

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