The expression I could not care less originally meant 'it would...

The expression I could not care less originally meant 'it would be impossible for me to care less than I do because I do not care at all'. It was originally a British saying and came to the US in the 1950s. It is senseless to transform it into the now-common I could care less. If you could care less, that means you care at least a little. The original is quite sarcastic and the other form is clearly nonsense.