AU where Dean’s a cop and Castiel is a private detective, and they always find themselves working on the same case, generally getting up in each other’s faces because Cas knows that the police are fucking useless and Dean thinks that the pretentious detective-dickhead-in-a-trench-coat needs to stop interfering with the law and mind his own fucking business. Somehow, extremely competitive and far-too-frequent angry sex ensues with name-calling becoming a regular occurrence (because neither of them will admit it, but the arguing really turns them on).