Mindless spewing of "good manners" for no other reason than that they're "good manners", without actually meaning the words coming out of one's mouth.
Case in point, the "thank you/you're welcome" issue. If someone is truly welcome, then I will let them know it. However, when they thank me for fixing their issues because they're too lazy to learn how to do their job properly, I do NOT feel that they are welcome. I will say "no problem" indicating that 1) they didn't really have a problem, they were just stupid. this is my own private joke. 2) it was not a burden to me to help them. 3) "no problem," is a form of polite acceptance of thanks, similar to "not to worry," "no worries," "forget about it," "don't mention it," etc. And as for saying "thank you", that's to express gratitude or acknowledgement. Why does that need to be expressed? Why do I need to acknowledge someone properly doing their job? Why does someone need to acknowledge me properly doing my job? When such phrases are overused, if someone actually DOES do something worthy of gratitude, it's kind of lost in the wash.
And the whole "bless you" thing when somone sneezes or coughs. Who does that person think they are, to be able to call upon a deity to intercede on behalf of someone else, just because there was too much pollen in the air?
I guess the actual peeve, from a larger perspective, is people being taught to do things by rote, without being taught the reasons WHY they are done. Which directly leads to people's brains being unable to think.