Red & Black Costume Devils Tail

Every now and then, you may hear of someone having a "devilish" look about them. But, when someone says that, what exactly are they referring to? Are they suggesting someone has a sharp goatee, sinister little horns, and a pointy tail? Or, maybe that they are deceptively good at fiddle playing? Perhaps, looking "devilish" is more of a state of mind rather than a literal style choice, and everyone has a devil inside them that they let out from time to time...