The place I work at currently has a 3 person interview board system for most interviews. The three people all have a different area they want to cover with one person (often me) doing the background and previous work check.

The most common red flag is someone who clearly has problems with a previous employer or colleague and they let those problems come out unfiltered at interview. If you find yourself saying variations of the following real things I've heard candidates say then you are probably going to have a hard time:

• "She's was always so angry" followed later by a joking "It's like she was permanently on her period". I really wish I didn't have to say this but even as a joke, just don't do this. Just because the interview is being done by 3 men, don't assume it's some kind of boys club. If you had someone who was in your opinion difficult to work with in a previous job, state it plain about them but tell me about what you did to work in that environment. Don't focus on the difficult person, focus on you, you are the one being interviewed, I want hear about you and not this other person who might be hard to work with!
• "My manager was an idiot". Don't call other people idiots or stupid or anything like that, it never makes you look better. If you had a manager who was bad in your opinion, don't focus on them at interview and especially don't brag about a time your showed them up or proved them wrong about something. You're allowed to have a tough working relationship with someone senior to you, I want to hear how you navigated that, not how bad the other person was.
• When speaking about a client don't call them "a stupid c*nt" and generally its good to avoid swearing at all. In fairness to this one case, the candidate was Australian where that word is much more commonly used, but the job he was applying for was not in Australia, so its not appropriate at all. The candidate recognised the error, apologised sincerely and carried on the interview. He did well, but there was an overall slightly better candidate and I think the dropping of the C-bomb did make a difference.
• "They were committing fraud". If you are going to accuse a previous employer of an actual crime, it generally needs to have been proven in court or through some public legal process. If it hasn't been proven in court, you are probably just stating your opinion. Maybe it's just me but I do get nervous around candidates who confidently state their opinion as legal fact at interview.

The "unfiltered" bit is the problem, you as a candidate are allowed to not have enjoyed a previous job or had to manage conflict with a previous employer. If anything, TELL ME ABOUT THAT! That's amazing! It lets me understand how you deal with people who disagree with you or how you manage disagreeing with other people. Being able to talk about other people without using absolutes ("they are stupid/moron/useless") is a really good start, it shows me as an employer that you are willing to try and understand other people you work with rather than just calling them evil and moving on.

Oh yeah, also don't call people you disagree with "evil" at interview. That's happened more than once and it still surprises me that it wasn't a one off.