Which is correct: could care less or couldn’t care less?

Let’s look at an example sentence:

The rebellious Sally could/couldn’t care less that she got her fiftieth detention.

Answer: couldn’t care less

If detentions truly don’t bother the rebellious Sally, then she couldn’t care less that she got another one. If she could care less, then it’s implying that she has a current level of caring that could be lowered.

When explaining that a level of caring equals zero, say couldn’t care less.

Here are more example sentences:

Danny couldn’t care less that he got a twenty-dollar parking ticket because he’s a millionaire.

The alien couldn’t care less that he was blind in one eye because he has thirty other eyes.

Sammy couldn’t care less that Fanny lost her Morrissey album because he hates Morrissey.