There is a lot of illegally shipped alcohol, which everyone gets's drunk and becomes rowdy. This was during the time prohibition was an illegal and organized crime involving "speakeasies" and such places that would smuggle alcohol. Many of guests were people who were usually dying to get in contact with Gatsby for maybe a job or some big break, they wanted to be rich and famous like him. It shows the "moral decay" and a huge amount of materialism that was running rampant in the 1920's when consumerism was on the rise. In the 1920's it was all fun and games until the huge economic depression of the 30's.
