Why do people say "I could care less" when they seem to be expressing the exact opposite, that they couldn't care less?

I think it’s gotten warped over the years, much like some people saying/typing “of” instead of “have” (“I should of gone to school.”) As soon as you point it out, people see that it’s incorrect, but by that time it’s become such an ingrained habit that it’s hard to break.

I don’t think it’s a regional thing; just one of those mistakes that happens (like people saying “fustrated”).

It’s a pet peeve of mine, and I sometimes can’t help myself – I have to point out that they are saying exactly the opposite of what they’re trying to express.

That, and “in close proximity”. To be proximal is by definition to be close.

I first heard this paradoxical usage in the early 1960s. I didn’t understand it then, either. Language evolves in weird and illogical ways.

Because they have it wrong.

“I could care less, but I don’t.”

Isn’t it the other way around?
People saying I couldn’t care less where they meant I could care less?

@rebbel Why would you say I could care less? Wouldn’t you say I couldn’t care more?

I meant the example given in the question: I thought people usually say couldn’t care when they mean could care.
I personally don’t say either, first because I don’t speak English that much, and if I do I simply say I don’t care.

@rebbel Oh, no, the expression is used to mean that you don’t give a flying fuck. But in a backwards kinda way, saying that you do give a flying fuck, instead of what you mean.

Now I am confused too :-)
I couldn’t care less though I could care and I do, but now I go to bed, it is 4:30 AM here.

My translation of the two expressions is this:
I couldn’t care less = I couldn’t care any less than I do right now, or in other words, I don’t give a flying fuck thank you Athaelflaed
whereas…
I could care less = I care to some degree so it would be possible for me to care less than I do

@rebbel And flying fucks are good. You would, say, want people to give a flying fuck about the groundbreaking research you’re doing in microbiology, or your sister to give a flying fuck about your divorce.

Grammatically speaking, using the expression “I could care less” is to sarcastically push someone or something away. It is also a way of saying, “I could, but I don’t care” (as others above have pointed out).

Saying “I couldn’t care less” is a way of saying “It is difficult for me to care less about this or that.”

I think people use the expression “I could care less” as a means to separate themselves from a source of anxiety, frustration, pain, etc. It’s like waving the white flag and surrendering. Others might use the phrase to politely say, “fuck off!” or whatever explicative way of telling someone to back off.

I’ve used the phrase in the past when I tried to individuate myself from my family. I cared too much about their approval. However, saying or thinking “I could care less” eventually conflicted with my heart. It wasn’t that I didn’t care for them or about them. It was that I was overwhelmed and needed boundaries. So, I started using a different phrase: “I care not to care.”

Saying “I care not to care,” felt like I was really saying: “I do care. I’m a caring person. I care for ______. But, and this is a big but, I choose not to care or hold onto the things that keep me from becoming me.”

I’ve never come across someone saying that they “could care less” who actually meant what they said. “I couldn’t care less” appears to be one of those phrases that are used so often people don’t think about what they’re saying, even when they end up using a mutated version.

In the UK I only hear “I couldn’t care less. I was always confused when I heard on American programmes or sites like this “I could care less”. Doesn’t make sense to me if you are trying to get across the message that you don’t care at all.

“I could/couldn’t care less” is interesting because it’s a phrase where the presence or absence of negation doesn’t seem to change the meaning. There are a few other examples of this, for instance:
Eddie knows squat about phrenology.
Eddie doesn’t know squat about phrenology.

That’ll teach you not to tease the alligators.
That’ll teach you to tease the alligators.

And more here: http://itre.cis.upenn.edu/~myl/languagelog/archives/000368.html