Since there has been a lot of discussion on interviews lately AND because I expect to be interviewing very soon, this question seems good.
What is your interviewing pet peeve? That one thing that a candidate does which sets you off and ensures the candidate won't get a job.
Mine is profanity. I recall interviewing a very good candidate one. If you consider a 1 to 10 scale, with 10 the best, this person was about a 7-8. Very solid and could have been pretty sure of getting the job. In one of the last questions, they slipped. The question required a discussion of something negative about a previous position and they said "For lack of a better description, it was just all f---ed up." They instantly went from the 7-8 down to a 3. What I heard was "well, I can't come up with an intelligent way to describe it, so I'll resort to vulgarities." Is this the way they expected to relate to a customer? In my opinion, there is never, never, never an excuse to curse.
Just sharing this - like turning off the cell phone, or having a clean desk, I guess the little things really do matter.