聞きかじり － could not care less / could care less - 実践ビジネス英語（12OCT2017)より

● could not care less = could care less
（どうてもいい、全く意に介さない）

does not care at all
She could not care less about money = that person has no concern about money

I could care less = I do not care at all

does not care at all

肯定形も否定形も同じ使い方をされる。