In the first half of the twentieth century, the influential American etiquette author Emily Post considered the term "gentleman" to mean a man with a superior standard of behavior. The word "gentle", originally meaning that a man came from a good family if not outright nobility, came to be associated with the standard of manners expected from that elevated origin. Later, the term was extended to include any man of good, courteous conduct.
Unfortunately, in recent years the term gentleman has been diluted further, so that it now is used to refer to males who are members of certain drinking clubs that offer lap dances by minimally clothed females but altogether lack manners. And a man's poor manners can be a serious impediment in his life, for, like appropriate dress, good manners serve as a social lubricant.
Now bad manners may not get a man murdered outright, though I've brightened more than one evening with the thought of what I'd like to do to the boor across the table from me, but they are likely to limit his interactions to his peers in what were once thought of as the lower social orders. And, depending on his choice of career, that can be a serious impediment to his success.
In my opinion, every man will benefit from reflection on the state of his manners, and, if his self-examination finds them wanting, from an effort to improve them. For each of us is responsible for the quality of life of those around us.
Be a gentleman.