Some types of jerk behavior are obvious. Calling names. Laughing at someone’s ideas. Stealing a coworker’s lunch out of the office refrigerator (come on, are you an animal?).
But it’s also possible to be a jerk by accident, especially in writing. Have you ever found yourself worrying that your two-sentence email will sound cold to the person on the other end? Or are you just now realizing that’s something you should worry about? (You should—warmth may be even more important than competence when it comes to establishing business relationships.)