I ride buses and subways. I will usually offer my seat to an elderly person, someone with a disability, or anyone who asks because they need to sit down. I do not consider pregnancy to be in the same category as disabled or elderly, so I don't normally offer my seat to pregnant women - but I would stand if I were asked.

One of the most annoying things in NYC is when people hold the trains' doors and keep them from closing. This causes the majority of instances when trains go out-of-service.