Shadowy Man

Now you can eat your cake and have it too!!

beastmaster

"I could care less" is the sarcastic form of "I couldn't care less." Both formulations are proper grammatically, although the former should be said with heavy eye-rolling or hammy exasperation in order to convey the sarcasm.

Chicken Girl

But "I couldn't care less" is already scarcastic.

DarkBronzePlant

Gotta disagree with both beastmaster and Chicken Girl here. "I couldn't care less" isn't sarcastic, since you are saying precisely what you mean. Sarcasm entails saying the exact opposite of what you mean, but in such a manner that it's obvious. Kind of like:
"Hmm... you're rude, lazy, fat and ugly. Yeah, I really want to go out with you!"
But "I could care less" isn't really a statement that lends itself to sarcasm. I don't think. Let me see:

*sigh* "I could care less."
or
*sigh* "I could care less."
I don't know. Maybe it works... But undoubtedly the majority of the people who use the phrase aren't trying to be sarcastic; they're just butchering the other phrase.

never been there

Oh, since we're all rolling in pedantry, you mean "ironic". It's a favorite way of being sarcastic, but they are not the same.

For example, to say to someone: "You always find the worst possible time to say something, don't you?" is sarcastic. "You always finde the best possible time to say something, don't you?" to the same person is ironic and sarcastic.

Cynical-Chick

No, sarcasm is meant to be mean/humorous.

DarkBronzePlant

Hmm. I'd always understood irony to be an understood component of sarcasm. I mean, come on folks, I should be an expert on the subject since I first learned about sarcasm from a Peanuts comic strip. (I know that was sarcasm! )