"The first rule is: you don't talk about it" is a reference to which movie?

The answer is Fight Club because the phrase "The first rule is you don't talk about it" is a recurrent line in the movie. This rule emphasizes the secretive underground nature of the Fight Club, a clandestine fight club that forms the central plot of the film. The rule signifies the importance of maintaining secrecy and confidentiality among its participants.