> BTW, it's "could not care less"
Oxford recognises "could care less" to mean "couldn't care less".
"I couldn't care less" is pretty new, first seen in mid 20th century. "I could care less" is newer, but has been in use since at least 1969.
This page has some interesting talk about Yiddish stress patterns. When you think about it you can imagine someone saying, sarcastically, with palms up and arms spread, "I could care less", meaning "As if there's anything in the world I could care less about".
BTW, it's "could not care less" as in "I could not possibly care less than I actually do". If you could care less that would mean that you do care. Sorry, personal pet peeve.