Rhinoceros [1974] Gene Wilder

A hungover Stanley meets his pompous and condescending best friend, John, at a restaurant. John's inevitable criticisms about Stanley's drinking and dishevelment are interrupted by a rhinoceros charging through the street outside. This provides the staff and the patrons some amusement until the creature charges through the restaurant and destroys everything. At the office, Stanley arrives late as the boss and the other workers are having an argument about the absurd news reports regarding these animals. The attractive but not overly bright Daisy insists she saw the rhinoceros with her own eyes. Stanley says the same thing, but it's not until a coworker on the street below changes into a rhinoceros before their eyes that they grasp the importance, and absurdity, of what is happening. Soon, everyone is becoming a rhinoceros, and Stanley is feeling the pressure to conform.