They're intoxicated by their personal styles. Styles learned in the movies, and from radio and the detective magazines. It's as if they were invented by Ben Hecht through his crime dialogue. Walter and Phyllis are pulp characters with little psychological depth, and that's the way Billy Wilder wants it. His best films are sardonic comedies, and in this one, Phyllis and Walter play a bad joke on themselves.
More genuine emotion is centered elsewhere.
It involves Neff's fear of discovery, and his feelings for Keyes. Edward G. Robinson plays the inspector as a nonconformist who loosens his tie, reclines on the office couch, smokes cheap cigars, and wants to make Neff his assistant. He's a father figure, or more. His investigation leads to two scenes of queasy tension. One is when Keyes invites Neff to his office, and then calls in a witness who saw Neff on the train.