I personally don't care how simple a question is or how well it's explained. If I walk into an interview with a portfolio full of samples and completed projects, and a resume full of references and qualifications, it's insulting and leaves me with a bad impression of the employer.
At one point in one of my first hiring experiences I was asked at the last minute to come sit in on interview of a candidate, and handle the technical part of it. This was for low-level driver development work. I hadn't seen his resume before, so I got a pretty bad shock when this candidate said at one point "I'm the maintainer of subsystem X in the Linux kernel". With a a laptop on hand, "cd ~/git/linux-2.6; grep -R candidate_name" revealed easily enough to verify he wasn't joking.
I bailed out of that interview, as I considered it grossly inappropriate to interview someone who was obviously much my senior in the relevant subject matter.
The more senior interviewers informed me afterwards that was a mistake. If the candidate is who he claims he is, it will be immediately obvious during the questions, you apologize profusely and all are happy. If that doesn't happen, you might have saved the company from a major screw-up. And that does happen.
TL;DR easier to apologize to a candidate than to to fire someone
