From Longman Dictionary of Contemporary Englishbe a devilbe a devilPERSUADE British English spoken used to persuade someone to do something they are not sure they should do Go on, be a devil, have another gin and tonic. → devil
Examples from the Corpus
be a devil• He is a devil from the conservative point of view.• There may be devils afoot, though not necessarily white.• It was almost as if there was a devil inside him.• Some people considered this stranger to be a devil changed into the illusion of an angel of light, or a witch. 