It's cruel to be kind

What's up with people these days? I see blogs of people bitching about the rudeness of others all over the web. This is just another one of those...with a twist. What I notice and hate is when someone does something nice for someone else and isn't acknowledged. The most obvious example of this is in traffic. I make it a point to try to let people in to traffic when we're not moving very much (and believe me, in McDonough, GA, that's a lot). Well, why don't people at least give you a little wave as just to say 'thanks'? I was raised in the South and taught from a very young age to be courteous to others whenever possible. I'm not perfect, but I sure try as often as I can. I just don't know why people just can say a little thanks for the kindness.