I've only heard it from Kiwis, but I am told it's used in other countries as well: "I can't be arsed" means (IIUC) "I can't be bothered". Where could the expression come from? It's the only expression I know of that uses "arse" as a verb -- assuming that is the correct spelling. Is it from "arse" (British English for "ass") or some weird mangling of "ask" or something even stranger?
Also, do the Brits even still say "arse"?
To make an effort to do something, you have to "get off your arse"!
Hence "can't be arsed" means don't feel it worthwhile to make the effort of standing up and doing something.
It is also heard in Britain.
It may be more the structure than the word "arse" that is at the origin of this. There are a few expressions where you can use a whole range of words, but the important thing is the structure. For example, you can put pretty much any past participle in the following and it will be understood to mean either "he was extremely drunk" or "he was extremely drugged" (or one or two other notions such as "tired"-- the point is there are a narrow range of interpretations compared to 'all the past participles in the universe'):
He was completely ...ed.
Or:
He was one ... short of a full ... .
with any pair of words that semantically go together will effectively be taken to mean "he wasn't very intelligent".
So similarly with "arsed", you can insert a wide variety of words (many of them expletives): "bothered", "fucked", "frigged", "buggered", "shagged". Indeed, if you say "I couldn't be jingled to do it" it would probably be interpreted in the same way. So it's not clear that there's some special meaning attached to "arsed" in this case.
We've always used arse rather than the American ass, but this expression is a recent British import. I'd actually be mildly surprised to hear it from a New Zealand-born person, and would suspect that they were consciously copying a phrase from a British comedy.
Can't be arsed dates from at the very least 1968, where it appeared in Hunter Davies' authorised biography of The Beatles, in a Paul McCartney quote:
"If they can't be arsed awaiting for me, I can't be arsed going after them. So I sat down and watched telly."
As semi-vulgar slang, it will have been used in speech much before first appearing in a book.
The OED has "can't be arsed" from 1988, and here's a verifiable Saturday, November 8, 1997 from The Times ("Go tell it to the fields - Profile" by Robert Crampton):
The previous night at the club, I had said to [Andy] McNab that I sensed he was slightly...bored? McNab had sat with his back to the stage, and seemed more eager to talk to his mates than to look at the girls. "I'd rather be chatting with them 'cos I haven't seen them. We land up there. They like it, I like it. It's fine when it happens, but I can't be arsed sitting there looking at them all night."
In answer to your question whether or not Brits say arse, an emphatic yes. We would never use the word ass to mean "backside" except in certain Americanisations like "a can of whoop-ass". Ass is used as a perjorative term (somewhat archaic) but I think in that context it relates to the animal.
I sometimes heard can’t be asked when I grew up in the North of the UK. I’ve no idea whether asked is a euphemism or arsed is a dysphemism.
