Could care less: Means you CAN care less. It means you could care a whole hell of a lot or very little. Doesn’t matter, just so long as there’s room to care less than you do. By saying this, you mean you DO care at least a little bit.
Couldn’t care less: Means you could not possibly care any less than you do. It is physically impossible because you give so little of a shit. There is not even a shred of caring in you. None. You do not give a single fuck.
Now, which one do you think you mean?