Just like the American "could care less" is the same as the British "couldn't care less". Two nations divided by a common language as someone is supposed to have said.
A better example of phrases that mean different things on either side of the Atlantic is what it means to "table" a proposal. In the US it means "kill it", but in the UK it means "bring it up". If an American says "could care less", they're just being incorrect. ;)
"could care less" is a shortening of "could not care less", and the latter phrase is correct. the words themselves don't mean anything any more, it's a stock phrase.
i think the sentiment is, "I care so little that I don't even want to use all the words needed to say how little I care".
How about, "I care so little that I can't even be bothered to properly pronounce that I couldn't care less."
or
"I could care less" is actually sarcasm which implicates that caring is obviously unlikely.
Both statements display a stronger degree of uncaring than "I couldn't care less" which is actually a pretty boring and to the point statement. Therefore I find "I could care less" to be the clear winner to indicate how little I actually care.
The common use of "nonplussed" means exactly the opposite of the intended meaning. It may be wrong, but it's generally understandable in context. I'd argue "could care less" works the same way.
