I could care less
It's a stupid mistake made by Americans who think they’re fancy. It's like saying 'I could be even less interested,' but no one gets it. People who use it are just trying to cover up how dumb they are.
'I could care less about your stupid opinion,' said the kid who didn’t even know what the opinion was about.
'I could care less about the movie,' said the kid who didn’t even watch it.
'I could care less about the test,' said the kid who didn’t even take it.