It's wrong to say bad things about your coworkers online.
Peter just had a horrible day at work after getting into an argument with a couple of his coworkers.
Peter wants to vent his frustrations.
Peter writes an email to his boss explaining his frustration and detailing his coworkers' behavior.
Peter makes a Facebook post about the argument he has with his coworkers and talks about them disparagingly.
Peter's boss invites Peter and his coworkers to his office and has a talk with all of them focused on resolving their issue.
Peter's boss sees the Facebook post and fires Peter since he believes it makes the company look bad.