Arriving late or arriving too early
If you are arriving late, you might as well skip the whole interview. If this is what you are doing on the job interview day then what will you do after you get the job?? Punctuality is very important. On the other hand, arriving too early will make you look desperate. It is best to arrive right on time.
Dressed up wrongly
The first impression the employer will get about you is from the way you look, and that will affect the rest of the interview. You need to dress up appropriately for the position you are applying for.
Not knowing basic information about the company
Having absolutely no idea about the company's products and services shows lack of interest. Interviewers like candidates who have researched the company before arriving to the interview because it shows enthusiasm.
Talk too much or not talk at all
There is nothing worse than interviewing someone who goes on and on... Keep your answers brief and direct to the point and don't interrupt the interviewer. On the other hand, answering everything by just "Yes" or "No" will not help either. Make sure to always say something informative and useful.
Failure to connect yourself to the job offered
You are a rocket scientist who recently lost his job and now you are applying for a job at McDonalds. The employer is not interested in your ability to fly shuttles around the moon. You need to link your knowledge to the offered job and show the interviewer how your experience relates to it. Don't talk about unrelated skills.
Not asking questions or asking too many
In the interview, you are the one who should be answering not the other way around. Keep your questions to a reasonable level and make sure they are directly related to the position. It is always good to ask at least one question.
Asking about salary too early
You don't want to sound too materialistic. The salary issue will come eventually. Wait for the interviewer to bring it up. Focus on presenting yourself as the best person for the job.
Attacking past employers
The world is small and you don't know who your interviewer might know, including your previous idiot boss. Keep your disagreements with your past manager to yourself.
Being too modest or too flashy
The interview is your chance to shine and highlight your abilities. Modesty is great thing but not during a job interview. Make sure to showcase your accomplishments and qualifications as best as you can.
That can be so annoying sometimes. It is a job interview, not your wedding night.
Failing to remember what you wrote on your own resume
Interviewer: "So, when did you graduate?". You: "1985". Interviewer: "It says 1986 on your resume". You: "It does?!". Ouch! Get out of there while you still have some dignity.
Complaining about anything!
Nobody wants to hire someone who is easily irritated. You have plenty of time later to suggest changes but for now stay cooperative and smile.
Even if you are, don't show it. It will make your position week. You will not be able to negotiate salary and benefits later.