"Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs, that it may benefit those who listen" (Eph 4:29-30).
The way you interact with fellow employees at work can often determine whether you will be the leaven for Christ in your workplace or be viewed as one of the multitudes. Two defining situations in the workplace involve joke-telling and discussions about employees and bosses.
If we laugh at off-color jokes we give permission to the person telling the joke that it is OK to continue this activity in your presence. If we fail to laugh, we discourage this behavior. When someone is about to tell a joke in my presence, I stop them and ask, "Is this a clean joke? If not, I don't want to hear it." This will define future situations with that person and it will get communicated to others in the office because of your response. You might become known as the religious person in your office, but that is OK.
The other situation that can define you is how your talk about management is in front of other employees. In a workplace it can easily become a "we" versus "them" culture. If this happens you violate Paul's command to honor those who employ you. "Teach slaves to be subject to their masters in everything, to try to please them, not to talk back to them, and not to steal from them, but to show that they can be fully trusted, so that in every way they will make the teaching about God our Savior attractive" (Titus 2:9-10).
"LORD, who may dwell in your sanctuary? Who may live on your holy hill? He whose walk is blameless and who does what is righteous, who speaks the truth from his heart and has no slander on his tongue, who does his neighbor no wrong and casts no slur on his fellowman" (Ps 15:1-3).
Remember, you are always a witness at work, whether you use words or not.