Altercations over polite behavior on public transportation offer a window on a changing society, reports Tang Yue.

If you're riding the bus or subway and see a pregnant woman, an elderly person or young child standing up in front of you, you might want to think seriously about offering them your seat.

If you don't, you may discover that the consequences are serious, given that a number of altercations have happened recently and some have even ended in violence.