A student recently asked the question, is it OK to say “I could care less”? This phrase can be confusing to non-native English speakers, because when taken literally it means ‘I have the ability to care less’ or ‘I care to some degree’. However, any native English speaker knows that when a moody teenager mumbles this to their parents as they roll their eyes, the idea is clearly ‘I don’t care at all’. It is easily recognized as the phrase ‘I could not care less’ with the ‘not’ being excluded, as if to emphasis the lack of caring.
Although the question is not about where the phrase came from, it is worth noting that the dropping of a word in a phrase is a common occurrence in casual English. It happens when something is awkward or a little difficult to say. It is the reason we use contractions in English. For example, ‘don’t’ is easier and quicker to say than ‘do not’. Because the mouth and tongue must work harder when the ‘not’ is in the phrase, it is altered for ease of pronunciation. Because ‘I could not care less’ became common enough as a phrase, omitting the ‘not’ became a habit of speakers and it was understood to mean the same thing. In fact now without the ‘not’, it is often given a sarcastic tone to emphasis the point being made.
According to the Oxford English Dictionary, ‘I could care less’ is considered an American colloquialism. ‘I could not care less’, was originally a British saying that was picked up by the Americans in the 1950’s, who started to drop the ‘not’. Because it is a casual phrase, this phrase is not appropriate to use in formal settings, such as business English. Some English speakers feel this is a sloppy pronunciation habit that should be avoided at all costs. However because the meaning of the phrase is widely understood with either pronunciation, really it is up to the speaker to chose to use it or not. In casual conversation with friends, it can be OK to use, in the sense that no one will misunderstand what you mean.
Sarcastic: Using words that mean the opposite of what you really are trying to say, especially in the case of insulting someone, showing irritation or trying to be funny.