From Longman Dictionary of Contemporary Englishwhat are you talking about?what are you talking about?spoken used when you think what someone has said is stupid or wrong What are you talking about? We got there in plenty of time. → talk
Examples from the Corpus
what are you talking about?• And I was like, I was just like, what are you talking about?• What are you talking about? - Ron has lots of money.• And, anyway, what are you talking about, the rich man in his castle? 