180 DEGREE RULE-DARK KNIGHT

The 180 degree rule is a very popular rule among directors

The 180 degree rule is a basic guideline in all film making, showing that two characters (or other elements) in the same scene should always have the same left/right relationship as to each other. If the camera passes over the imaginary axis connecting the two subjects, it is called crossing the line, therefor breaking the 180 degree rule. The new shot, from the opposite side, is known as a reverse angle.

DARK KNIGHT
During the interrogation scene between the Joker and Batman in the film 'Dark Knight' Christopher Nolan, the director broke the 180 degree rule,however it worked because i realised when ever the joker is having a conversation with batman or another "good" guy, the camera breaks the 180 degree rule (i think intentionally), to display the disorder of the jokers character, i.e. the breaking of camera rules shows how the joker breaks rules.
Also, in the conversation between the two characters the Joker Say's 'tonight you're gonna break your own rule'. To me, this phrase directly links to the 180 degree rule being broken, making it cleverly fitting to the scene.