Green Tortoise is RIGHT in the middle of the strip-club district.
It's not dangerous really, but LOUD well into the night (talking 3am).
Fisherman's Wharf is pretty nice, as is the downtown one which is close to Union Square/cable cars/BART station.
Tenderloin's not too bad, just poorer than most of the city. Lot of homeless running around there but it's also home to some of the best Indian/Pakistani and Vietnamese restaurants in the city. Just be aware and you'll be fine.
I grew up just outside of SFO.. lemme know if you need more advice...