Whenever someone says "I could care less" to me in real life I have to stop the conversation in order to clarify what they mean. "Are you saying you don't care at all? Or are you saying that you actually care somewhat? Or are you aware of the ambiguity implicit in that phrase and are thus using it ironically in order to be deliberately ambiguous?"

Yeah usually I'm all let and let live when it comes to language mistakes and differences in dialect, but this one actively hinders communication so it's kind of failing at being language.