I couldn’t care less whether it rains today or not.
That means that if it rains or it doesn’t, I really have no room to care any less than I do either way.
Now, if I said I could care less — which we hear so often — then what’s really the point? If we can care less than we do, we’re not really making any statement worth the time to make it. We could just as easily say, “I could care more.”
So, if you couldn’t care less, that’s cool. If you could, then don’t bother.