We're getting quite off topic from antonyms, but:

> “I could care less” is a bastardization of couldn’t care less.

I've come to the conclusion that this bastardization came from the way "--dn't c--" feels in the mouth. Lots of consonant sounds in a row. Drop the "n't" and it feels much better to say, even though the phrase becomes nonsense. You even get a little bonus alliteration.