OK, here is one of my biggest pet peeves:
A customer walks into the store and gravitates (usually) towards the Wave Music System. I tell them a little bit about it, play a little music. They seemed a little confused as to whether it is actually something they want or need. In an effort to help them out and do a proper needs assessment for them I ask, “So where were you planning on putting the system?”
They answer, “IN MY HOUSE,” as if I actually thought out on the lawn next to the garden knome was one of the options.
At that point in the conversation, no matter how nice the person was before that, it takes all the energy I can muster not to smack them upside the head and shout, “NO SHIT, SHERLOCK!”
C'est Non Un Blog 
My biggest pet peeve at my old job was this scenerio: I’m wearing a uniform, I have on a name tag, I have a microphone in my hand talking about the place and WHILE I’m speaking a person comes over and asks: “Do you work here?” I can’t tell you how many times this happened and how often I wished I could say: WTF do you think? Sometimes I’d say “no” and then wait a few seconds and laugh and then say “just joking – how can I help you?” The masses are asses.
What was your old job?
I was an “educator” at a very large zoological organization. 😉 Part of my job was to give educational lectures about the animals at the exhibits. It was pretty obvious I worked there!