Union definitely has the reputation of being a party school. Wednesdays are the new Thursdays. That is when everyone goes out just because it works into most people's class schedules better. Monday is also becoming a "go out" night, but Wednesdays, Fridays, and Saturdays are usually when you will see the most students out at night. Chet's on-campus bar is open Monday (in the spring), Wednesday (always), and Friday for happy hour (always).
Students will usually drink somewhere with friends (depending on your age) and then go to Rupsis or Geppetto's (if they are looking for a bar). If you don't drink, there are usually non-alcohol related activities happening around Union from campus movies (which show every weekend) to concerts and comedians. If you look for it, you can find it. There are students who choose not to drink, and no one really pressures them to get wasted, though many students choose to drink. The comedians are great, and the movies are usually pretty good, but don't expect to find many `cool' parties late Friday or Saturday night without alcohol being served.