A brain fart
/ə ˈbreɪn fɑːt/very informal, crudeUK · US
What does “A brain fart” mean?
A brain fart means a brief lapse in memory, attention or judgement
Forgetting your own postcode at a counter might prompt “Sorry, brain fart.” The speaker is treating the lapse as brief and unimportant.
It can also mock a foolish idea. For a polite apology, “I lost my train of thought” or “I made a mistake” is safer.
When do people say it?
A crude, joking way to describe a small mental slip. Most suitable for laughing at your own mistake among people you know well.
“I had a brain fart and forgot my own postcode at the counter.”
Is it formal or informal?
Register: very informal, crude. It is most at home in everyday conversation rather than formal writing. Most common in UK and US.
Where does it come from?
The phrase jokingly treats a momentary failure of thought as an embarrassing bodily noise. It is deliberately silly and crude.
Origin confidence: Disputed; treat with caution
How do you say “A brain fart” in other languages?
Last updated 2026-10-01