English is a living language, meaning that it’s always changing, always evolving. Unless you want to live in constant pedantic frustration, you have to be willing to accept new words or phrases that didn’t exist at all in the near past or, a bit harder, words or phrases that originally meant one thing but have now come to mean something else because of common misuse or a general misunderstanding. Think of decimate, which technically means the destruction of around ten percent of something but is commonly used to imply complete and total devastation. Or irregardless, which actually isn’t a word at all but one that many people employ instead of the correct regardless.
I consider myself open to change, and I can roll with the punches with a barely perceptible wince. However, one phrase that is commonly misused grates on my nerves every single time I hear it spoken or read it in a book to the point of jolting me from the conversation or story. I’m talking, of course, about the dreaded “I could care less.” The phrase is correctly, “I couldn’t care less.” My problem with this wrong phrase is that in using it, the speaker is saying the exact opposite of what he or she actually means.
I’ll let Dave Mitchell explain it – his version is much more entertaining and done in a delightful British accent.