On that same note, do not be a hero, use the pole or other available handles while the train is moving. Your natural sense of balance and soft ski knees are no match for an urban metro driver. If you accidentally fall in to the lap of a passenger while holding on to a pole you might be forgiven. However if you bump in to a fellow rider because you were stupid enough not to hold on to the pole, Lord help you.
The Folding Seats: This can be a real point of tension. Use of the folding seats is a treat only to be enjoyed if the train is relatively empty. As soon as the car starts to fill up you MUST surrender your privileged seats so your knees are not driving in to the crowd in front of you. This creates more space for more people to grab on to the bar (using one hand) and pack in around the door.
Misbehaving on the metro can result in a sharp elbow in the back, an exasperated sigh, a dirty look, an eye roll or a nasty combination of these things. Children and tourists are not given any slack.