I was in New York in March 2001, celebrating my fortieth birthday with my wife and a couple of friends. We had lunch in the restaurant on top of one of the towers (Window to the World?) and on the way back out my friend and I had our shoes shined in the mall at the bottom.
I pissed off the bloke who shined my shoes, because I didn't tip him at first. When I got outside, my mate pointed out my error and I turned to see him staring at me. I felt absolutely terrible - of course, the tips were a lifeline to these guys and I should have known instead of being a typical tourist prick. I went back, apologised, and gave him a generous thank you.
I watched the towers go down live on TV six months later. The shoe-shine guy came to me immediately, I just hope he was one of the lucky ones. I can see his face clear as day now. The staff in the restaurant, probably not so lucky.
I know it probably sounds a tenuous link to some, but this day (9/11) is always a poignant day for me.