I have said, to a lot of people, who have said "I could care less"... "so you care".... none have yet understood what I meant.... without additional explanation
Either way, the phrase is illogical anyway. There's no way to adequately quantify someone's amount of "care" in concrete, measurable terms, so whether one says "I couldn't care less" or "I could care less," the entire phrase is utterly pointless to begin with.