My boss comes in, takes a seat, and doesn’t want to pursue the applicant further. Why? Because he was a jerk to the receptionists, and that interaction was part of the interview.
Any interaction that you have with a company, and the people that make up the company is fair game for the selection process. Even if you’re having a bad day, and the non-technical HR rep interviewing you keeps spelling out S Q L instead of saying SQL, you’ve got to keep your game face on. All interactions ARE the interview process.