Ephesians 4:29 (NKJV)
Let no corrupt word proceed out of your mouth, but what is good for necessary edification, that it may impart grace to the hearers.
A few years back, I was doing some training at one of our offices and was poking a little fun at one of our employees. Later, one of my partners invited me lo lunch and we got talking about things of the Lord. It was a delightful lunch. Near the end of our meal my friend quoted this verse to me and mentioned that I had hurt this employee's feelings. All of a sudden I was under great conviction of my sin. I quickly made restitution and thanked my friend for his rebuke. Now, I try lo rehearse this verse at the beginning of every day.
Notice that bad language or hurtful statements (both apply) not only affect others but make you unclean as well. See what Jesus has to say about it:
Matthew 15:11 (NIV)
What goes into a man's mouth does not make him "unclean," but what comes out of his mouth, that is what makes him "unclean."