"Sitcom," above all, requires a large grain of salt: it is visually shocking and provocative, and American audiences in particular often dismiss it as a "vulgar" film on these grounds. The plot, however, contains an allegorical richness that is rarely attained in most modern films. It is a theater of the absurd, and must be understood as such in order to comprehend the complexity of meanings and social commentaries it has to offer.
For starters, it is a criticism on the most basic level of the social alienated embodied by bourgeois social standards in France. One of the most accessible aspects of this commentary is the unwillingness of the characters to genuinely communicate to one another. While this makes several scenes totally hilarious, at the same time it micro-cosmically calls into question the validity of a "coherent" unit to address its internal problems; this is, obviously, an allegorical reference to France as a nation. The nation--like this bizarrely self-contained familial unit--is unable to progress and modernize in accordance with modern needs because of a lack of communication. The abstract issues of race, homosexuality, insanity, and even modern psychiatry are called into question. The modern cannot be a museumization of the past, despite whatever aesthetic benefits such staticness might offer.
It would be a good idea before viewing this film to read Freud's "Totem and Taboo." Despite the fact that no scholarly connections between the film and this work in particular have been made, it provides at least some provocative insight into the plot. I would also suggest against making a viewing of this film a family event; it would be most appropriate among those of an older age group, and is a particularly provocative piece of French film.