If you are interested in what the British Aristocracy is all about, or more specifically, what are the external signs of an aristocrat, try to get your hands on a copy of this book. It is a lively exploration of the quaint turns of phrase, social peculiarities, and other habits that identify the British upper-classes (charmingly referred to as U), as distinguished from the lower-classes (non-U).
As the title suggests, what makes an aristocrat is a sense of Noblesse Oblige, or the obligation of the nobility to put his high position at the service of those beneath him, and at the service of the common good. That being said, there is always a je ne sais quoi about the fictional and non-fictional characters of the Aristocracy that make them sometimes irresistible and other times loathsome, but always fascinating, and often extremely funny.
If you simply want to know for the sake of idle curiosity--or if you want to avoid the blunders (beginning with audible self-promotion and ending with obnoxious table manners) that might make the occasional aristocrat you run into at a dinner party either enjoy your conversation (think of Elizabeth Bennet) or avoid you like the plague, (think of Mr. Collins) you will enjoy this book.
If you are a sociologist studying the nature of class-distinctions which the human race routinely creates (in spite of every attempt to prevent it) than you will REALLY enjoy this book.
If, on the other hand, the very thought of social class gives you hives, avoid this book at all costs.