What people who criticize others are hiding
Those who criticize everyone but themselves fall into one of these two camps:
1. They love to highlight what they perceive as other people's flaws and shortcomings as a way of hiding their own.
2. They lack self-esteem and do this in order to feel better about themselves.
Some of my coworkers, who are otherwise nice and caring people, have a penchant for talking smack about people's clothes, work habits, and overall lifestyle.
When this happens, I just nod along and proceed to change the subject. I refuse to be dragged into the chorus of backstabbing, always keeping in mind that they could use my remarks against me at any point.
People should keep their unflattering comments about others to themselves -- plain and simple. What do they gain by disparaging people whom they may know little about?
At the end of the day, we don't really know a person's battles (at least not all of them). Maybe they dress or act a certain way for a reason. We should always resist the impulse to single out a person for being different in some way.
Even if the reasons for lambasting the person seem justified, e.g., he belittles subordinates or makes inappropriate comments about minorities, you're just stooping to his level by joining the fray.
A better approach would be to advise a supervisor and arrange a closed-door meeting to address his unbecoming behavior. Chances are he'll be fired or reprimanded, prompting him to clean up his act.
If you ever feel prodded to join in on the bashing, hold your ground. Even if it gives your coworkers pause, they'll know they can't weasel you into doing whatever fancies them. And, always remember -- misery really enjoys company.