As @jonah found out, it's just a joke–only the "existentialist breakfast" is a real thing that probably started as a joke, and that I've seen on one or two menu

As @jonah found out, it's just a joke–only the "existentialist breakfast" is a real thing that probably started as a joke, and that I've seen on one or two menus of cafes willing to skirt the rules on selling pharmaceuticals. But the joke is most definitely not "on you". As in: It wasn't meant to expose anybody's shocking lack of knowledge of arcane Australian trivia.