Minor note:
If you could care less about something, you are implying that there the thing in question has some measureable degree of importance, however slim, in that it is possible for that degree of importance to lessen.
If, on the other hand, you couldn't care less, you are describing a situation in which the object of your disdain has sunk so low that it is impossible to imagine being able to have any less interest in it.
It's an important distinction. Thankyou.
Some time ago heard this explained as irony. In other words, she says she could care less, but anyone listening should know better.
This is a method used frequently in the Calculus to prove that a function is a minimum.
Have to agree with Christian Murphy. When the "wrong" phrase is used by articulate people, it's often meant to be taken as sarcasm. Imagine it to be, "Like I could care less."
Now explain how "head over heels" means inverted, or I'll rant about the misusage of effect vs. affect.
The "irony" explanation comes from Steven Pinker in The Language Instinct. (There could be other sources, but I've read it there.) Personally, I don't think that people mean it ironically; one hears "I could care less" far too often for that to be true. I think it's simply become a stock phrase that people use without parsing. Grammarians and purists put far more stock in "logical" usage than empiricial evidence suggests is supported by actual utterances.
There's a good song by Ben Folds Five on the subject of who could care less ... can't remember the name tho.
And, today's "spot-the-reference" award _almost_ goes to Cameron. The song is called "Battle of Who Could Care Less", and it's off Ben Folds Five's "Whatever and Ever Amen".
The lyrics are here: http://www.benfoldsfive.com/lyrics/whatever_10.html