My husband has a habit of saying, when he cares very little about something, "I could care less." Being an editor and writer I am anxious to inform him that his statement is incorrect and he should say, "I couldn't care less." He gives me a funny stare, as if the proper grammar is any bit important. He knows that I understand his lack of concern whether he says the statement correctly or not.
To help clarify I have located a "the caring continuum." He gets it now. Thankfully I won't have to subject his speech to anymore correction, that is, until he ends a sentence with a preposition...eeww! Actually he knows better.