Unwittingly, you have destroyed your chances. Nowadays employers get feedback on a candidate from anybody whom he had met. If the potential recruiting manager comes to know of this harmless comment on your present boss, you will be labeled an undesirable element.
Here are a few tips to help you stay careful:
Don't be relaxed: Many career coaches point out that it is a myth to believe that interviewees should be relaxed during the interview. If you think that you are not being scanned, you end up making disastrous mistakes. If you appear to be relaxed, the interviewer may get an impression that you aren't bothered whether you get the job or not.
In your attempt to show that you are comfortable and relaxed, you may sit back in the chair and the potential employer gets the wrong signal. The moment you think the job is yours, you start behaving as if you landed the job and you forget you are a candidate seeking the job. Don't think the interviewer is your best friend. He isn't. You must keep the distance.
An interview is no different from your first date; follow the first-date-rule to put your best foot forward. Be cautious; if you are not, you may end up talking about distasteful things. Don't talk about your personal woes.
Don't babble: When you are nervous, you talk too much and in the process you discuss irrelevant things. To get out of such a situation you have to prepare for the interview. Jot down a few questions that you can ask the interviewer. It isn't a bad idea to have a mock interview.
Be early to the interview: Most of us don't keep time to check our appearance. Keep time to visit the wash room and check how your looks are. For that you must be at the interview site at least 15 minutes early. Stretch your muscles to release any tension.
Be polite: If you are rude to anyone at the place of interview, the potential employer may get a wind of it and you create a bad impression in the mind of the interviewer.
Don't drink: Sometimes interviews are held over lunch or dinner or at some social functions where alcohol is available. Career counselor's advice goes against touching alcoholic beverages. Just say you drink occasionally, "today I prefer iced tea".
Shun hot topics: Avoid religion, politics and other controversial topics. Don't think you will appear smart if you touch topics like same-sex marriages or some other controversies.