Basic Trope: Two police officers (or similar) interrogate a suspect by taking on different personas; the 'good' cop who acts reasonable, and the 'bad' cop who acts aggressive.
Straight: Bob and Carl interrogate Eddie, their murder suspect. Bob acts calm and reasonable, suggesting that it's better for Eddie that he confess; Carl acts aggressive, hinting that he's willing to beat it out of Eddie if necessary.
Bob is incredibly gentle, almost pleading with Eddie; Carl practically has to be dragged off Eddie.
It isn't an act. Carl really is that aggressive, and Bob is desperately trying to restrain his behavior.
Downplayed: Bob is polite and Carl isn't.
One cop acting aggressive and intimidating the suspect makes it possible that the suspect will gravitate towards the more reasonable seeming cop in order to secure a confession.
Bob and Carl are two criminals who interrogate Eddie, a cop, in this fashion in order to discover how much their criminal enterprise has been compromised.
When being interrogated, Eddie acts incredible aggressive and hostile towards Carl, but mild and meek with Bob.
Carl acts incredibly aggressive towards Eddie, making it seem as if Bob will be the good cop. Bob, however, is the Worse Cop, and acts even more aggressive and confrontational than Carl did.
Both Bob and Carl are reasonable and cool-headed.
Carl intimates that Bob will be even worse than he was, but Bob is still playing the good cop.
Bob emphasizes the good parts of cooperating in his talks, while Carl insinuates what may befall him if he refuses to cooperate. Both do so in a calm manner, making Carl able to unnerve Eddie by discussing almost nonchalantly things like known perps already in prison that wouldn't hesitate to gut Eddie like a fish.
Bob and Carl have trouble keeping which 'cop' they're supposed to be straight, and keep switching.
Bob is too nice, and / or Carl is too aggressive.
Bob and Carl push the concept a little too far, and begin indulging in other types of 'cops', with the result that the suspect is hit with such combos as 'Absent Minded Cop / Overly Fastidious Cop'. The suspect is a bit bewildered to say the least.
Zig Zagged: Bob and Carl switch over who is the good cop and who is the bad cop.
Averted: Bob and Carl use interrogation techniques other than this one.
Lampshaded: "Oh come on — are you guys seriously doing the whole 'good cop / bad cop' thing with me?"
Before the interrogation, Bob and Carl agree to try 'good cop / bad cop' on the perp and agree on their roles beforehand.
Da Chief makes Bob and Carl partners, because he knows there personalties will let them do this.
Exploited: Basically every time it is in use.
Defied: The suspect is a career criminal who has been arrested multiple times and is prepared for the standard police interrogation tactics, meaning that Bob and Carl will have to search their playbook for a tactic more likely to work.
Discussed: "Everyone's heard of it, but you'd be surprised how often 'good cop / bad cop' works — you really would."
Conversed: "Are there any other interrogation tactics than 'good cop / bad cop'?
Deconstructed: Because of the popularity of television shows using this trope, criminals who are arrested are prepared and almost expect the 'good cop / bad cop' routine, making Bob and Carl's life more difficult.
Reconstructed: Just because the perps expect it doesn't necessarily mean it still can't be effective from time to time, however; particularly with suspects who, while they might have seen a lot of cop shows, are not prepared for the actuality of being in a genuine police interrogation.
Bob: "Why not go back to Good Cop/Bad Cop? It'll be easier for you and all of us if you do." Carl: "And if you don't, punk, I'll bounce you off the walls, you dig?"