What Would You Do?

Last night on our way home from dinner, Nick and I were walking down Lexington Ave a few blocks from our apartment. It was 9pm and there were many people out walking the streets, eating in restaurants and drinking in bars. All of a sudden, in the middle of a busy sidewalk, we see a white male with a 3-foot metal rod in his hands, prying a horseshoe-shaped bicycle lock hooked around the bar of a bicycle and a lamp post. As Nick and I literally walked by this man, within about a foot of distance between him and us, he was prying and pulling and prying some more, to the point at which he was grunting and gritting. For a split second I thought there was a chance this man had just lost the key to his lock and was trying to get it off.
But no. I said to Nick, "I think that guy is stealing that bike, right in front of everybody!" I stopped to watch this event unfold a few feet away from where I was standing.
And then POP, the man snapped the lock off and grabbed the bike. I said to Nick, "Oh my God, that guy just stole that bike! In front of all these people!" Nick responded, "Yep, that pretty much is exactly what just happened." We stood there, watching this man steal a bike. And if there was any doubt left in our mind whether the bike was his or not, we watched him fall over as soon as he attempted to mount the bike and ride away, because it was obviously way too big for him. And to make clear that Nick and I were not the only bystanders allowing this to happen right in front of us without saying or doing anything, there were about 10 other people who stopped and stared exactly as we did in disbelief.
We walked away feeling like huge jerks, that we just witnessed somebody steal somebody else's property and didn't say a word. Nick affirmed, "Well that's New York for you."
Here we are, witness to a crime, and we do nothing. But what would you do if you saw a man with a 3-foot crow bar, who probaby was on drugs, who was obviously a criminal, and you had nothing to defend yourself from a 3-foot metal weapon but your hands?
Seriously, what would you do?