"Anti-Social"

Have you met anyone who is anti-social? No matter what you ask them to do, or where to go, the answer always come back "no." Sometimes I wonder if they are leading a double life or trying to hide something? Or maybe they are just too afraid to be seen with someone so un-cool? So maybe they are stuck- up? Shy? Reserved? It gets annoying after a while, when you make all efforts to include these people in events or outings -- only to realize that you've wasted your energy and breath. I wonder why anti-social people are this way? A genetic trait or an acquired personality? Are they just trying to be nice not to hurt you by staying out of your way, or if they really have a problem?