Hint: if you’re talking to a writer or editor, even on social media, try hard to get this phrase right. Heck, if you’re talking to anyone, it’s worth knowing the difference.
If you couldn’t care less about something, that means that you already care so little about the subject that it’s impossible for you to be interested in it even less than you already are. I couldn’t care less about calculus. Or glittering vampires. Or most forms of reality tv. (Sorry, but it’s true).
If you could care less about something, then that means that you do indeed care about it. You maybe aren’t singing it from the rooftops, but there’s room for less interest. And maybe you are singing it from the rooftops; that’s possible too.
This is a writing and speaking tip really. I have faith you can get it right. I’d say I couldn’t care less if you do, but I just do. I really, really do.