Question: “Is it sinful for Christians to use vulgar language?”
Answer: I want to avoid being legalistic on one side of this issue, and also avoid being libertine on the other side. On the one hand, I've always been amazed by Christians that will use God's name in flippant and irreverent ways, breaking one of the ten commandments, and then react with shock and disgust when someone utters a crude word. In the halls of divine justice, saying a phrase like “Oh, God!” to express dismay and disgust is a far, far more grievous offense of God’s law than the dropping of the infamous “F-bomb” in a sentence. I'm always fascinated by how words evolve into vulgarity, why some words are considered so rebellious (or how some words, like "sucks," evolve from vulgarity into normal usage). The whole thing seems silly to me, as does the need that so many people have to insert one of these “shock-effect” words in the place of every adjective and adverb that they need in a sentence.
At the same time, I think that we should be careful about the standards for the language that we use. Paul, in Ephesians 5:1-4, addresses this subject directly: “Be imitators of God, therefore, as dearly loved children...But among you there must not be even a hint of sexual immorality, or of any kind of impurity, or of greed, because these are improper for God's holy people. Nor should there be obscenity, foolish talk or coarse joking, which are out of place, but rather thanksgiving.” What is “obscenity, foolish talk, or coarse joking?” Even in Greek these terms are vague. Obviously, the definition of those terms will vary from culture to culture and age to age, just as the definition of “modesty.” However, vagueness doesn't vacate the words of any meaning. They do apply to some portion of our English language. So, what portion is it?
I don’t see anywhere in Scripture where the use of vulgar language is condoned. In Philippians 3:8 Paul uses the word translated as “dung” or “rubbish” (literally...“what is thrown to the dogs”), but there's no evidence that the term that he used was considered “dirty” or “vulgar” in his culture. It was a colorful, valid, and socially acceptable synonym for “worthless.”
But, to some people’s surprise, the Bible doesn’t give a list of seven or ten “dirty” words that we are to avoid. Words that describe body parts, bodily functions, or sexual behavior aren’t inherently dirty or obscene. God created all of those things and declared them good. The sin lies in the intent behind the words. Our culture creates dirty words by debasing and demeaning these good things that God made.
It seems to me that we as Christians are expected to be sensitive to the language of our culture and be aware of what is considered dirty, raunchy, and obscene by our peers, and then avoid the use of it, for the sake of our holiness and witness to Christ. Earlier in Ephesians 4, Paul says, "Do not let any unwholesome [corrupt, worthless] 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." To me, vulgar words all seem to be about projecting an image and having a self-centered purpose. I can't see another person's heart, but I have to be honest – almost every time I hear a Christian use foul language it appears to me that there's an element of rebelliousness to it, or they're just trying to impress me or someone else with how “cool” they are. I can’t ever remember hearing a vulgar word used for the purpose of building another person up according to their need.