I couldn't care less
US /aɪ ˈkʊdnt kɛr lɛs/
UK /aɪ ˈkʊdnt kɛr lɛs/

1.
全く気にしない, どうでもいい
used to express that one does not care at all about something
:
•
He was complaining about his new car, but I couldn't care less.
彼は新しい車について不平を言っていたが、私は全く気にしなかった。
•
Whether they come or not, I couldn't care less.
彼らが来ようが来まいが、私は全く気にしない。