To the OP directly, don't get your self into a situation like that above.
Well, I am sure this is true for some percentage (perhaps even large), it isn't a rule to live by... Never look like a victim, but don't assume that an "air of confidence" is a bullet proof vest either... This appears to be a common practice - flagging victims down with a relatively polite demeanor and then sucker punching them...
I had a similar thing happen when I was a kid only the assailants were in a minivan and I was on a bike. I realized after the fact, that they were upset that I had seen them driving away after robbing a house in the middle of the night (I was training by riding a bike in the wee hours of the morning in a large gated community).
I often wonder what I would have done if I were armed, but unless they were as well (I'll never know), I am sure it would have ended badly for me...
It was even worse than some of the hypo's here because each of the three of them were pretty small compared to me. They only managed to land one punch in the whole process and I was unfazed by it (not unbruised, but unfazed). He was reaching up so far to hit my head that it hurt, but it didn't have enough force to matter...
In the end, I pushed the three of them off balance with my bike and got out of there. It was dark, I was outnumbered and unarmed.
In my mind the threat I faced was deadly - Had I stayed and fought, I know I had enough of an advantage to do some damage, perhaps even take them all down, but the reality of 3:1 on even with training is that even a slight misjudgment and you are down. Once you are down, the kicking starts and the mortal wounds start...
But, you don't need to look far to realize that most juries who haven't experienced this are looking for something sharp or shooty before they can justify the victim's use of lethal force. UNLESS there is a size disparity - which as I mentioned, would not have worked in my favor. Compared to any one of them, I'd look like an ogre if I it gone to court...
The other lesson I learned from this is that as an individual, the police can NEVER protect YOU. You are a statistic waiting to happen. The police can protect the community (i.e. the "next guy" your perp assaults), but not you. By the time you are a "victim". It's too late for the police to help...