I was spat on once too. But it was when I was younger and my sister, who was in the front passenger seat decided to spit out the window and it (spittle?) came in the back window where I sat.

But seriously...
All in all, you need to weigh in all the factors involved in Ultra-G's scenario.
1. He was alone and there where 5 of them.
2. He's in NYC...enough said (although they say the crime rat has gone down tremendously).
3. It was night, less chance for witnesses.

Now with these factors we need to answer the following questions before any act of retribution can be carried out.

1. Did he know if they were "packing"?
2. Does Ultra-G have any self defense knowledge or experience?
3. Was Ultra-G harmed or was his life threatened in any way?

I would have to say no to #1 & 3 as I don't know if Ultra-G does indeed have any knowledge of self defense other than the knife he carries around.

If I was in his shoes, I would have been pissed! Majorly! But, even with my knowledge of TKD and self defense, I don't think I could have taken on all five. I don't think being spat on deserves retalliation. Like someone said, these were probably teenage kids doing what rebellious teenage kids do when amongst their peers. Simply attacking 5 defenseless little boys (that's how their lawyers will describe them) with a knife who were just doing foolish things as they gallavanted across the bridge on their way home from a night of joyous frollicking and then getting sued because of the irrepairable (sp?) damage you caused their psyche isn't really worth all the trouble now is it?

On the other hand, if my life were threatened in any way and there was no reasonable way out of it, then you'd better watch out cuz I'm not going down without a fight.