couldn't care less
Meaning: You can say "I couldn't care less" when you don't care about something, or it doesn't matter to you.
- Tim thinks we're all interested in what he thinks, but we couldn't care less what he thinks, to be honest.
- Most people couldn't care less about the problems of people on the other side of the world. They've got their own problems to worry about.
Occasionally we hear "could care less" as well. This is used to mean the same thing, even though it looks like it should mean the opposite. Some people think this variation appeared when people misheard the original idiom and started saying "could" instead of "couldn't". The strength of this argument is that "could care less" doesn't make a lot of sense within the context of its use, whereas "couldn't care less" makes perfect sense, as in "I care so little already that I couldn't possibly care less than I do."
Yuki said she couldn't care less about
- her husband's illness
- her daughter's exam results
- the weather in Switzerland