> Merriam-Webster treats the phrases couldn't care less and could care less as synonymous, both meaning "not concerned or interested at all." "Couldn't care less" is the older and more obvious phrase grammatically, but it has been confused for so long that both are now defined.

Thanks for your feedback. However, I’m going to stick with Webster on this one. Let’s also not forget that English has always been a hodgepodge of language mashups and slang.

https://www.merriam-webster.com/words-at-play/could-couldnt-...