1. Being late. While occasional lateness may be excused in other situations, it's often a deal-breaker in a job interview. Hiring managers assume that you're on your best behavior while interviewing, so if you aren't on time for the interview, they'll assume you'll be unreliable if they hire you. Always allow more time than you'll need to travel so that you have a buffer in case something goes wrong.
2. Badmouthing a former employer. As tempting as it might be to explain that you left your last job because your boss was crazy or that your previous company was mismanaged and corrupt, sharing these feelings will reflect badly on you. Rightly or wrongly, the interviewing convention is that you don't badmouth a previous employer. Hiring managers are looking for evidence that you know what is and isn't appropriate to say in business situations.
3. Not being prepared with examples that illustrate why you'd excel at the job. If you claim that you excel at strategizing or that you're an innovative genius, but then aren't able to give specific examples of how you've used these skills, interviewers aren't going to give much credence to your claims. Make sure to come to the interview prepared with specific examples from your past that show how you've turned your skills into real accomplishments at work.
4. Telling an off-color joke. Interviewers are scrutinizing you for evidence of what kind of judgment you have. No matter how friendly your interviewer might seem, inappropriate jokes or off-color language have no place in a job interview. You'll call your judgment into question, and will make your interviewer wonder what you'll be like when your guard is down after you have the job.
5. Not asking any questions. You might be spending eight hours a day in this job, at this company, with this manager. Are you sure there's nothing you're wondering about? Interviewers want to know that you're interested in the details of the job, the department in which you'll be working, the supervisor's management style, and the culture of the organization. Otherwise, you're signaling that you're either not that interested or that you just haven't thought much about it. So come prepared with thoughtful, intelligent questions about the work you'd be doing.
6. Sounding bitter. Job-searching is tough, and it's easy to feel discouraged. But if you sound even the tiniest bit bitter or negative about your job search or a previous employer, you'll turn off potential employers and almost guarantee that you won't get offers. No one wants to hire someone who seems angry or resentful.
7. Not being likeable. Interviewers are human and want to work with pleasant people. If you're unfriendly, arrogant, or rude, it won't matter how qualified you are; interviewers won't want to hire you. So be friendly and open, and show genuine interest in the people with whom you're talking. Don't feel you have to hide your personality, or be so formal that you become stiff or impersonal
Alison Green writes the popular Ask a Manager blog, where she dispenses advice on career, job search, and management issues. She's also the co-author of Managing to Change the World: The Nonprofit Manager's Guide to Getting Results, and former chief of staff of a successful nonprofit organization, where she oversaw day-to-day staff management, hiring, firing, and employee development.