I guess it's mood-dependent for me. I don't get my feelings hurt easily, so if someone doesn't wave back, I am typically annoyed, not embarrassed, for about half a second until my ADD kicks in and saves me.

Whether I wave or not also kind of depends on what model they are driving. Some models are more conducive to a real enthusiast who loves every aspect of owning and driving an amazing car, versus an average shmo with a status car. If they don't wave back, it's their loss. Sometime too, they don't see the wave until the last second and it's too late. I have done that a couple times in deep thought while driving (doesn't happen often).

 

By the time it usually registers with me they are already past so I probably look like a snob= not intentional and do wave back when I notice.

 

Got the thumbs up by a BMW driver going by in the carpool lane.