I confess, I don't see how that would make it reasonable to act like an incompetent jerk. You can "pass" the interview and decline the job offer.

Or just politely say, "Now that I'm here, I can really see this is not the opportunity for me. Let's not waste any more time. Good day."

We're all lovely people and we served nice coffee and delicious biscuits.

eww, biscuits!

I think that sometimes happens subconsciously. People internally don't want to the job and tank the interview.