“So who should be most brassed off by this show?”–Jason Farago, New York Times, June 1, 2023, in reference to “It’s Pablo-Matic,” an exhibition at the Brooklyn Museum, which he did not like.
When I came to the phrase I’ve put in italics, it sounded like a Britishism, and it is. Green’s Dictionary of Slang defines it as “irritated, fed up, annoyed,” and has two 1940 citations, one from a book called A. A. S. F. (Advanced Air Striking Force, by Charles Gardner: “Cobber said he was ‘brassed-off,’ especially after he had got half-way home once, only to be called back to hand over his flight and teach two new-comers the way around.” Neither Green’s nor the OED has anything to say about etymology, but it would appear to be a combination of the verb “brass off,” meaning to complain, which is seen in British service slang as early as 1925 and “browned off,” meaning annoyed, which popped up no later than 1931.
Observers at the time had some fun describing the differences among those two phrases and another new one, “cheesed off.” A 1943 Time magazine article on RAF slang reported: “Among thousands of Americans, ‘browned off’ already means fed up. (‘Brassed off’ means very fed up and ‘cheesed off’ is utterly disgusted.)”
And a 1943 book called Women at War had these index entries:
“Brassed Off. See Browned Off.
“Browned Off. See Cheesed Off.
“Cheesed Off. See Brassed Off.”
In Britain, “brassed off” got pretty popular pretty fast. A short story by Herbert Bates which was published in a 1942 book has this passage:
He spent most of the rest of his life being brassed off.
“Good morning , Dibden, ” you would say. “How goes it?”
“Pretty much brassed off, old boy.”
“Oh, what’s wrong?”
“Just brassed off, that’s all. Just brassed off.”
In Britain, the phrase fell off in popularity after the War, but started picking up again in the 1980s, as this Ngram Viewer chart shows:
In 2004, the BBC ran a TV series called Brassed Off Britain, which endeavored to identify the things the country found most annoying. (Junk mail “won,” followed closely by banks and call centres.)
But the phrase has never taken hold in America. Until the line from Jason Farago quoted above, it had never been used in the New York Times by an American writer or source, except in reference to Brassed Off, described by the Times as “a funny and poignant  film set in a bleak Yorkshire mining town.” Similarly, it does not show up at all in the Corpus of American Historical English or from any American sources in News on the Web (NOW), a corpus of more than 17 billion words published since 2010.
So well done, Jason Farago! You have perpetrated a true One-Off Britishism.