The honest answer? You'll probably be fine. You'll also probably be bored out of your mind.

Let's separate the two issues, because they're both real. On safety: downtown SF late at night isn't the warzone that viral Twitter clips suggest, but it's not exactly a stroll through the Presidio either. Violent street crime targeting random pedestrians remains relatively uncommon compared to cities in Latin America or even some other American metros. The bigger concern is property crime — smash-and-grabs, opportunistic phone snatches, the stuff that happens when someone's stumbling out of a bar at last call not paying attention.