I agree with that, old bean, and I think A-train's cell phone idea is the best. Heck, even if you don't have a cameera on your phone, you can always bluff.
But then it's one thing to say you'd walk on by, another to do it. there are cases where I know I'd get involved; in fact, this is a fear of mine. This is one of the ways I could end up leaving China against my will.
This summer I was at a seedy bar late at night with a female friend when a guy we know came in and offered her a ride home; she was very drunk and didn't want to be alone with him in his car, so politely declined. He kept up the hard sell, then left. She expressed to me her relief that he was gone... then he returned and started in on her again. By this time she was sitting very still with her hands in her lap, staring at her feet, so I called her over, said she was free to do whatever she wanted, and asked her what she wanted to do. She replied that she didn't want to be alone with him, and he was scaring her. he approached her again, this time with me standing right there, so I said "____, it isn't going to happen." He angrily replied that he wanted to hear that from her, and then she said so. He sotrmed out, she thanked me, and got into a cab.
The next day he had a mutual friend call me and inform me that I had 2 weeks to leave Suzhou or he'd have some guys make me disappear. Being a rich kid, his family apparently has just the connections it takes to have this done. Being my first death threat, I was quite upset by it.
It's blown over now, but there's a lesson in it: in this case, seedy things happen in seedy places. I figured a Chinese guy would figure she and I were a couple and back off, whereas a foreigner would, at worst, start a fight with me. I didn't anticipate a Chinese guy that was partly raised in America threatening me with goons. That's why I stay out of bars now- that and I figured it best to stay out of his way.