I make a judgement call - either I end the interview immediately or skip most of the rest of the interview, let them think they made it all the way through the interview and say that we will get back to them with a decision later. When I end it immediately they usually take it badly but these are times that I just can’t justify wasting any more time on them. The bad reactions run the normal gamut of bad human reactions: angry, sad, indifferent, humor, etc.
> [I] let them think they made it all the way through the interview
Maybe then, although they get rejected later, they still won't be particularly upset at your company -- since the in person interaction was friendly and positive (i suppose), and you can take some time and write a friendly rejection email or phone call too (i suppose you have a template)
