I couldn’t care less
couldn't care less
Does not care about something at all. Fine, I couldn't care less what you do! Good riddance! You're going out with my ex-boyfriend? Great. I couldn't care less.
I could(n’t) care less
sent. I don’t care!; I don’t care to the maximum amount, and it is, therefore, impossible to care any less. (The affirmative version does not make sense, but is widely used, nonetheless.) So you’re late. I couldn’t care less.