This happens in long lines sometimes. People get antsy. Being in a big city there are a lot of foreigners who have a different concept of personal space. It really depends on the culture.
I'll admit I have pushed people (with my body not my hands) before when making my way through a subway train. I learned that when I was living in Asia. Often times people will all try to stand near the doors and not towards the center of the train car. It's very annoying. So I smoosh my way through the crowd to get to the center where it was less crowded. Think I pissed off one woman once. Oh well, I don't feel bad.