Japanese equivalent of a brain fart

Question

Is there a Japanese equivalent term(s) to describe a brain fart/absentmindedness? I noticed the term karahenji in Jisho.

Answer 1

ど忘{わす}れ is a word that, like "brain fart," means roughly that you are unable to recall something in the moment, but you would normally be able to recall it easily.

It comes from 忘{わす}れる (to forget) and ど, a prefix that can be used for emphasis or to add a derogatory tone to something.

As noted by kimi Tanaka in a comment, it's possible that there is a difference in register between the two terms across languages, since "fart" is not a polite word, but in meaning they are very close to each other.

Answer 2

According to Merriam Webster's dictionary, I use them for the explanation and please look up the bold part of my interpretation for the reference.

The definition of absentmindedness is the following :

Definition of absentminded

• 1 a : lost in thought and unaware of one's surroundings or actions :

was too absentminded to notice what time it was

ぼんやりし過{す}ぎて、何時{なんじ}か気付{きづ}かなかった

• 1 b : tending to forget or fail to notice things : given to absence of mind

Her absentminded husband forgot their anniversary.

うっかり屋{や}の旦那{だんな}は、記念日{きねんび}を忘{わす}れていた

I think this is what you are mentioning:

• 2 indicative of or resulting from preoccupation or absence of mind

gave an absentminded reply

空返事【からへんじ】をした。

If your brain-fart's usage is similar, I guess the explanation above is good enough.

Answer 3

If I'm not having a brain fart, that word can be used when wrong things come out off your head, as well as when nothing comes out.

ど忘れ in @Leebo's answer serves well for the latter case that you can recall nothing normally you should, but cannot cover the situation when you've said something nonsensical because of mental glitch. In that case I think I'd use ぼけて（い）る.

Explained with this Urban Dictionary example:

Person A: Hey, switch on the TV, this show is annoying.
テレビつけて。この番組嫌だ。
Person B: Switch it ON?
つける？
Person A: No, I meant off... I had a brainfart.
違う、消して。ぼけてたわ…

ぼける is an informal word to mean you have any kind of dementia, and also for thinko. If you blame for low consciousness (e.g. tired, sleepy...) you can also use 寝ぼける.