Social skills can vary greatly from person to person. This is especially true among the young. Some people are simply very introverted, and such a trait can be quite common from adolescence and into early adulthood. For these types of individuals, it takes every bit of courage they can muster to look someone directly in the eye when speaking, and this can particularly hold true when the recipient is of the opposite gender.
Because of hormonal changes that take place during these years, teens are often very self-conscious and tend to take everything they hear literally. If someone goes out of his or her way to make note of that big, juicy zit on your nose or tells you that your hair is greasy and lifeless, your self-esteem will be deflated. Those who are bullied, either physically or verbally, can be trapped in a seemingly inescapable shell of insecurity.
Fortunately, as people grow older, most will shed these feelings of inadequacy and open up. More mature individuals exhibit compassion and tact, which in turn reinforces feelings of self-worth on the part of those persecuted in the past. Most importantly, the typical adult is also far less superficial and shallow than his or her teenaged counterpart. Noticable changes may get off to a slow start, but gradually, the inhibitions of most shy people tend to fade.
And yet, a part of one's past will always remain. For example, some people may still rarely smile. When around strangers, they may still not speak until spoken to. When holding a conversation with a physically attractive member of the opposite gender, such people will continue to become a bit tense. In turn, this can give others a false impression of being rude, even when this is not the case at all. There is a very fine line between shyness and giving one the impression that you are unsociable and rude.
Thus, if you find yourself in a social setting and stumble upon someone who doesn't have much to say, it does not necessarily mean that he or she is being rude. One must take into consideration the fact that there are many individuals out there who had less-than-desirable social experiences during their formative years. On the other hand, if a person walks away from you in the middle of conversation, completely ignores you, begins to talk with somebody else, or responds with hostile or inappropriate comments, then certainly he or she is truly rude. Sadly, everyone will occasionally find people who fall into this category.
As for the rest who don't initially appear to be outgoing, give them the benefit of the doubt. Allow a little extra time for things to open up, for these are the very building blocks for relationships at every level.