I have no idea. I did however recognize the dialogue immediately. Next you should do the scene from When Harry Met Sally, if you haven't already....

The wheat toast.... at the risk of sounding pretentious, it represents Dupea's desire to stand as an individual and his struggle against the forces of conformity. The idea that something as prosaic as wheat toast should be too string a request to those whose minds have been conditioned to conform to the rules is telling. No substitutions, no exceptions.

Pliny, that's very much how I saw it. The toast is only a symptom. The condition is the no substitutions rule. And Dupea is struggling claim his own identity, not that which he's supposed to have, so this interaction with the waitress is taps into a deeper emotional dynamic he's confronting on conscious and unconscious levels.