From Longman Dictionary of Contemporary Englishwho cares?who cares?spokenDON'T CARE used to say that something does not worry or upset you because it is not important It’s rather old and scruffy, but who cares? → care
Examples from the Corpus
who cares?• Because with so much money, who cares?• The cisterns run empty by July if we're lucky, and who cares?• The point is that every teacher who cares about being a fine teacher has an identification with these principles.• Butterflies - who cares? also has its first showing at Kelvingrove - and will run until 20 June.• Am I the only one, he asked himself, who cares anything for Durkin?• It is an issue for anyone who cares for the sanctity of human life.• Who cares if some 19,000 voters in Palm Beach County were effectively disenfranchised?• Who cares? the President replied. 