I say "thank you" all the time. I was raised to be polite. You would say, please, thank you, pardon me, etc or you'd get a whack up side the head. What bugs me is when I say "Thank you" and some one says "umm hmmm". What is that? Does that mean "piss off, you're lucky I helped you"? Or does it mean you're too lazy to say "you're welcome"? I first noticed this years ago in Los Angeles whenever I said "thank you" to someone black. I know, you're all saying "that's racist", no it's not racist, it's a statement and an opinion and using the term black allows me to identify a segment of the population. I've just started noticing white people doing that "umm hmmm" thing. Clearly this problem is spreading and we need to stop it.
The origin of the whole "Thank you" and "you're welcome" back and forth began in the middle ages with "wilcume" meaning "I'm pleased you came" That morphed into when someone arrived at your home they were "well come", i.e. we're pleased you came. Somewhere in those centuries it morphed as a response to "thank you". They might not have had proper hygiene and plumbing back then but at least they were polite. And just to clarify - "No problem", "think nothing of it", and "it was nothing" are not equivalent nor appropriate responses to "thank you". The sense in you're welcome is one of "it was pleasing to me to do" whatever it was that you were thanked for.
Now is that so hard?
Today - practice your common courtesy. A warm smile, holding the door open and a "thank you" and "you're welcome" goes a long way in making it just a little easier to get through the day.