I will help you to ‘t. But tell me true, are you not mad indeed, or do you but counterfeit?

– William Shakespeare

Twelfth Night, Act 4, Scene 2. Feste, in his disguise of the priest Sir Topas, asks Malvolio if he is really crazy or just acting. But it is really Feste, who has just performed a mock exorcism on Malvolio to banish his supposed demons, that is the big fake here.