I've spent plenty of time musing about the lack of etiquette (see the award-winning "License and Registration, Please" 3-part series) already, but now we must spend a minute on misplaced and/or phony efforts of gratitude.
Please please please stop the excessive use of "Thank You" at the office. I feel like I hear "thank you" and "thanks" so damn much during the day that it puts that circa-1999 Alanis Morissette song in my head (you know, the one with the piano background, the one where she went pseudo-nude in the music video and officially jumped the shark). I understand being courteous and all, but it's gone over the top. You don't need to thank me for simply doing my job - I get a paycheck deposited into my bank account every Friday that serves that purpose.
It's even at the point that I see a ton of people with "Thanks," preceding their default email signatures. So you're telling me that you find it necessary to thank someone every single time you send an email? Half the emails I send at work involve telling people how or why they've just screwed something up, followed by detailed backup and explicit instructions on how to unscrew the situation. You can bet your last dime those emails do not include the words "thank you" at the end, because I do not believe in thanking people for being inadequate and wasting my time.
Thanking people at every turn, regardless of the quality of their actions, is a fertility drug for mediocrity. It's like having "4th-place" or "Participant" ribbons hanging up on your wall as a kid, or your parents slapping onto the fridge a science test with a nice 80 on it. People should be thanked for exceeding expectations, not for going through the motions. Those who overuse phrases of gratitude are either way too easy to please, or they operate on autopilot and don't pay enough attention to what comes out of their mouth. But maybe I'm the weird one.