The Undie Run takes place every year during finals so the students can relieve some finals stress. From the Los Angeles Times:
“One of the greatest college traditions in America — the UCLA Undie Run — takes place in the middle of the school’s quarterly finals. Thousands of Bruins bare (almost) all and run through campus in a moment of organized rebellion. The event, which occurred on Wednesday night, is intended to alleviate the pressure that comes with big exams.
Student bodies want to look their best, so underwear sales in Westwood Village spike in the run-up. American Apparel is a popular pick, but they’re not the blue-and-gold standard. Victoria’s Secret doubles their business on the big day, and they have better sales figures than on Black Friday (or “Pink Friday,” as they like to call it).”