What to do in San Francisco on a Friday night?

My friends and I are going to SF on a Friday night for my birthday. We won't get there until around 6pm, so museums and that are out. And we don't want to go to any clubs or bars. We'll be taking BART so we won't be driving around the city. Some ideas I had were Ghiradelli Square, Union Square, Pier 39, and Fisherman's Wharf. What do you suggest?