[This story contains spoilers for “Vanitas,” the fourth episode of The Audacity on AMC .] We’re going to break the first rule of Fight Club and talk about the fight club that marks the (slightly disturbing) climax of “Vanitas,” the midpoint of The Audacity’ s first season . For starters, it’s based on a real thing. “That’s what’s crazy,” Billy Magnussen , who stars in the AMC series as tech CEO Duncan Park, tells The Hollywood Reporter . “There were articles about it — there was an underground Silicon Valley fight club. People were in their offices all day, clicking away at the computer — I can see why they’d have pent-up aggression.” Duncan ends up at the show’s version of the club as part of his continued effort to land a nine-figure investment from valley legend Carl Bardolph (Zach Galifianakis) — which has thus far only resulted in Bardolph stabbing Duncan’s hand with a fork and having his security tackle Duncan the next time he approached.…