To have a 'Halley Cropper' is to have performed an act which is perhaps indecent, stupid or inapropriate. The term is derived from the popular coronation street character. For instance if u have had a Halley Cropper, you've had an absoloute shocker
Doug drops his drink on the floor after having too many.
His acquinatnce exclaims 'you have had an absoloute Halley Cropper their'