Right after 9/11, people in NY generally were a lot nicer to one another. I would say that NYers continue to be nicer to this day, but nothing like how it was after 9/11.
As far as myself...I feel like in order to live in a big city, you need a certain attitude. You can't be a pushover (this is especially true with us NYC teachers!) and need to stand up for yourself often. I like to help locals and tourists on the streets if they need it, but if someone ever messed with me, they'd get it. There's a difference between being mean and having an attitude. It's just second nature for me to stand up for myself. I teach in a run-down neighborhood in the south Bronx, and one woman was giving me problems for no reason (sitting beside her). She kept telling me to go sit somewhere else and I told her no. You can't let people walk all over you here. I joke around and say that someday I'm going to get shot since I stand up to anyone who tries to do/say anything to me, lol. But I know the right and wrong times to do it. It doesn't matter where I live, I'll still have this same personality trait. It's your typical "NY attitude"