I've run across some who will say "Thank you. Ta." at each turn of the transaction, managing to say it between 5 and 15 times in just a minute. After a while, it just doesn't feel like it means anything. What annoys me is an employee who will barge past you without so much as a 'get the hell out of my way', or make you wait while they barge past, then you get to the till, and it is the same person, with the whole 'polite' "thank you" thing. It feels as though some people pick and choose when to be polite. I'm all for please and thank you, but sometimes it just feels like an empty word when it said too often in a short time.
At our local chippy, one of the women will stand there and sing out "Thank you" to people to signal she is available to serve them. It took me a while to figure out what she was doing, and apparently the locals didn't know either. It is her version of "May I help you", or "Next please".
ETA: Funny story about the pudding. I happened to learn that one while still talking to hubby online before actually meeting. I will never forget the first time his mum came to visit and we were at a restaurant. After eating, she told the waitress "We'd like to order some pudding now". The waitress said something along the lines of "We don't have pudding, but here is the dessert menu."