Let's start a revolution! Let's start thanking people, and maybe it will spread?
What used to be common courtesy seems to have disappeared (along with some "common sense"?).
I try to make a point of thanking the check-out clerks (and pointing out when they do something excellent, like NOT putting all the breakable glass bottles in the same plastic bag! Or giving me change the old-fashioned way: coins first, then bills on top, so it's easy to manage them with one hand, NOT bills, then change on top, which means I have to juggle things to get the change/bills where they belong).
Even if you aren't doing something because you expect the thanks, it does make human relations better. I've held doors open for families who look overburdened (going a bit out of my way to do it) and not had them even acknowledge it (as if they feel its something that they are entitled to?). Makes me want to yell "YOUR WELCOME!" or to not do the same for the next people.