The beloved “undie run” at Colorado State University might be banned, but that didn't stop some students from partaking in the revelry. Hundreds of students ditched their clothes to run around the school's campus in just their underwear. The tradition of the "undie run” began 11 years ago on the last day of regular classes as a way for students to blow off steam before studying for finals. The first year, just a handful of nearly naked coeds took part, but it's grown over the years.