The idea of the Gentleman grew out of the traditions of knighthood in a very dangerous period of history.
While the concepts of knighthood and honor have long been out of fashion, some of the behaviors from that time still have meaning and purpose. The core concepts of the knight and the gentleman are similar: Protect the weak and defenseless, show compassion and mercy, speak the truth, and be courteous to others, especially women.
So what are some of the actual behaviors of a true modern gentleman?
A gentleman holds the door for others to go in. He definitely opens the door for women and lets them go through first.