Dawn Dugan specializes in writing books, articles, white papers, reports and special communications for the human resources industry. She is the co-author of Effective Executive Compensation, which was published by AMACOM in 2008. Read more...
A good rule of thumb is all body movements that result in sound are strictly verboten.
Cracking knuckles or other body parts is not polite, and sends the message you are incredibly nervous. It also indicates you have difficulty controlling your impulses.
Chances are, the interviewer will opt for a more socially aware, confident candidate.