What happened to the courtesy wave?!

I've been noticing a lot lately that people aren't giving a courtesy wave when appropriate.  For instance, when another driver lets you in a lane in heavy traffic, you should courtesy wave.  As a pedestrian, if a driver stops to let you cross the street, you should courtesy.  These are just a couple examples. 

Now, I realize that lifting your hand and giving a slight wave could be a bit strenuous.  I mean, you could have just come from the gym or maybe you just changed 100 light bulbs and your arms are really tired.  But suck it up, and give a little wave.  Or maybe someone put super glue on your steering wheel.  Then give a nod or something.  It's just polite and courteous and helps our society maintain a certain level of kindness. 

We have to acknowledge the smallest acts of kindness before they are completely absent from society.  So please, continue to give a courtesy wave, even if you're not sure it's necessary.  The world will thank you for it.