The Tenderloin isn't the best of neighborhoods and can get quite rowdy at night. I wouldn't recommend walking in it if you are unfamilliar with the area, intoxicated, and especially walking alone at night. During the day there are just a lot of bum's haning around, but not too much crime. Otherwise, it's not terribly bad. P.s. no matter how badly the look, don't ever give money to the bums.