http://articles.chicagotribune.com/2013-03-13/features/ct-tribu-words-work-care-less-20130313_1_care-harry-styles-idioms

Harvard linguist Stephen Pinker contends that rather than being willfully ignorant, folks who opt for "could care less" are being ironic or sarcastic, according to Fogarty.

British etymologist Michael Quinion agrees.

"It is so clearly logical nonsense that to condemn it for being so misses the point," Quinion writes on his World Wide Words blog. "The intent is obviously sarcastic — the speaker is really saying, 'As if there was something in the world that I care less about.'

Quinion compares the saying to some popular Yiddish phrases.

"Perhaps the best known is 'I should be so lucky!' in which the real sense is often 'I have no hope of being so lucky,'" he contends. "There are other American expressions that have a similar sarcastic inversion of apparent sense, such as 'Tell me about it!,' which usually means 'Don't tell me about it, because I know all about it already.'"