As the party progresses in chapter two of "The Great Gatsby," Myrtle gets more and more inebriated and begins to loudly make fun of Daisy after Tom gives her a puppy. The scene ends when Tom, angry at her behavior, punches her, breaking her nose.
The scene illustrates the major themes of F. Scott Fitzgerald's masterpiece, namely the hypocrisy and shallow nature of what he'd dubbed "The Jazz Age society." Myrtle, a married woman, begins the affair with Tom after meeting him as a stranger on the train. She is described as sensuous and is portrayed as someone who wants a life her husband cannot afford.
Tom is also married, and when Myrtle insults his wife Daisy by making fun of her, his defense is hypocritical. He is also callous in his treatment of Myrtle when he punches her nose. It underscores Fitzgerald's overarching theme that the rich use and trample on the lives of the poor. It fits with the economic uncertainties of the post-WWI time period that occurred just before the stock market crash of 1929 and the subsequent Great Depression.
The party scene itself illustrates the ambiguous nature of all the revelries. The people only seem to be able to have fun when they get drunk, revealing the desperate edge to the times.