There are times when I can’t return the wave because my hand is needed elsewhere. It’s good to be social, but sometimes I really need to use the clutch. Don’t take it the wrong way if somebody doesn’t wave back. They may not have seen it, they may have needed their attention or their hand elsewhere. Or maybe they think you’re a jagoff and not worth the trouble. No way to know, no point in getting fussed about something that probably doesn’t have anything to do with you.