1. In a group interview setting where each person had a series of questions designed to elicit different characteristics of the role, the candidate aced the first 2 sections. When he came to me, my questions were far more abstract and asked for some application of his experience. He wasn't able to cope, and what seemed to have been leaning his way suddenly eliminated him from consideration.

2. Someone who stumbled through finding the words to address even simple questions about the "type of role" (not specifics of the role I was hiring), and couldn't form a complete sentence. The question was simply, for a Project Management role, "Tell me in a nutshell about your project management experience."

3. The guy that babbled through an answer on a phone interview and then after about 3 or so minutes, came back and asked "I'm sorry can you remind me of the original question?"

4. Not being in the right frame of mind for a discussion. This includes blanking on a very basic question (see #2 above).

5. Thinking that the hiring conversation was "all about them" rather than "all about the personality match" or "all about the rapport established".

And in responding if the candidate asks about the outcome, I'll simply say that we've not selected them in the process and have chosen either "a different direction" or "have chosen a candidate who appeared a better match for the role and culture or the organization". As a candidate, that is feedback that brings closure to the situation and lets them move on rather than avoiding the question or saying "the position (that probably didn't exist anyway) has been put on hold"; as a hiring manager, that answer doesn't damage the organization. It's as much of a win as I think you could take away, and it's candid without being rude or blunt. TJNTIY.