I love the subway; I ride it every day and never tire of it. It is intrinsic to the experience of living in New York City, and is justifiably romanticized. But there are vagaries of conduct on the underground trains that cannot always be anticipated. For example, courtesy dictates that one give one's seat up to the elderly, to the infirm, and to women who are with child.
But with such opportunities for chivalry and kindness come great dangers. For if said woman is, in her opinion and to her knowledge, neither ill, nor elderly, nor pregnant, you will have just communicated to her that either her appearance is sickly, her visage is aged, or her midsection appears to be portentously distended. Please be advised: If such an error has been made, you will not have made a new friend of this stranger on the subway.