I was born in New York City, grew up in L.A., started a company in SF, and live in Chicago, but the only place I've ever been held up at gunpoint was in San Francisco at 4th and Mission.
That sounds like bad luck. Within San Francisco, 4th and Mission seems like one of the less likely places to be held up at gunpoint since it's so busy.
What are your reasons, out of curiosity? I'm a reasonably-sized guy, so I rarely feel personally scared, but I don't have to look far to see some really sketchy situations.