[phendrenad2]

As the interviewer, you should stick to an interview checklist, even if the candidate is obviously failing.

As the interviewee, nobody is keeping you there, if you're failing the interview and want to leave, just leave. Fly free little bird!

(Hopefully there were two interviewers, so the lone interviewer won't have to look bad when they tell their boss "The candidate left early and declined to reschedule", but if not, not your problem, sucks to be them).