This cliché sees to throw people for a loop. The right phrase is, “I couldn’t care less.” Because if you “could care less,” you are caring some.
Still want more proof?
From the The American Heritage Dictionary of Idioms, “This expression originated about 1940 in Britain and for a time invariably used couldn’t. About 1960 could was occasionally substituted, and today both versions are used with approximately equal frequency, despite their being antonyms.”