From Longman Dictionary of Contemporary Englishwhat/who/why etc the devil?what/who/why etc the devil?SURPRISEDANNOY old-fashioned spoken used to show that you are surprised or annoyed How the devil should I know what she’s thinking? → devil
Examples from the Corpus
what/who/why etc the devil?• What the devil are you getting at?• What the devil does he want?• What the devil have you been doing to yourself?• What the devil was he talking about?• Why the devil do you think I came haring over here?• Why the devil was she so stubborn?• Now what the devil was he to do?• So who the devil are these two engaging, literate, drug-free chatterers sitting down the pub? 