I really hate the en_US idiom "could care less". It means the exact opposite of the intended meaning of "couldn't care less" and it is confusing to people who have never heard that idiom before, or who have only heard the correct version ("couldn't care less"). It's just unnecessarily confusing and ambiguous to say the exact opposite of what you mean instead of just saying "couldn't care less". I actually didn't know about the "could care less" variant until I read the explanation of the xkcd about it (which I initially completely misinterpreted because I didn't know "could care less" was an actual idiom and not a mistake)