The title is the correct phrase when used to demote that you’re not bothered or interested in something.
It bugs me when I see I COULD care less instead.
Think about it for a moment. If you really do not care one bit about something then you really COULDN’T care less even if you wanted to.
If you COULD care less, then that means that you care at least somewhat doesn’t it?
So really I could care less if you couldn’t care less.
Have a good day now.