> Of course you can explain that the job wasn't a good fit, but in an interview situation you want to avoid opening the door for follow-up questions that will force you to choose to either make yourself look unprofessional (or too fussy) or to blame the former employer.
It is not unprofessional to end up in a situation where what you are asked to do is not in line with what you want for your career. Employers rarely put their employees career development first.
Note that I agree with you that ranting and needlessly badmouthing a company never reflects positively on someone. I just disagree that you should always be positive.
> Then he launched into a long explanation of how he didn't get along with his manager and how some of the other people on his team were slackers and so on.
That’s because venting frustration never looks good during an interview. But it would probably have been fine to say that as he was getting older, maybe he had a daughter, maybe he had some kind of epiphany, he was starting to feel uneasy about the porn industry and that it affected is ability to fit in the team. That’s not positive but that’s shifting the perspective from blaming other to a change in yourself which is a legitimate reason to search a new job.
In the same way, I wouldn’t necessarily look badly on someone who left a small company after four months and explained to me that they are actually looking for a place with more established processes because at their point in their career they are looking to learn the best practices and not put them in place from scratch and they misjudged the state of the company they worked for. That’s basically telling you were working for an immature but you shifting the discussion towards you and what you are looking for.