I was asked recently what I think about swearing. Is it ever appropriate? Is gosh a good substitute for taking the Lord's name in vain? Isn't it sometimes helpful to accent your point in a culturally understood way like swearing?
That kind of thing.
So, is using strong language ever appropriate? Some words, yes. An example would be damn. Paul uses the Greek equivalent in Galatians 1:8 in an edifying way. Ezekiel is quite graphic in his language (23:20). The awfulness of sin and error occasionally calls for referring to that damned Arianism or the whorish nature of idolatry.
The problem is that we are full of ourselves and think that if we are speaking it must be important enough to justify pretty much whatever crass word we want to say. This is as true for the adolescent impressing his friends with the shock, as it is for the proud and sophomoric writer, or theologian who wants to make his point with some "edginess."
Ephesians 4:29; 5:3-4
"Let no corrupt word proceed out of your mouth, but what is good for necessary edification, that it may impart grace to the hearers.... But fornication and all uncleanness or covetousness, let it not even be named among you, as is fitting for saints; neither filthiness, nor foolish talking, nor coarse jesting, which are not fitting, but rather giving of thanks."
Intent matters a great deal in this area. Are you meaning to impress, shock, or make a point? Then you're doing it wrong. Sinning, actually, I would say, by violating the Scripture above. The point is to help along the character of those with whom you are speaking, not to jerk their attention back to you, not drag their minds to the gutter to be wowed by your "earthiness" or worldly-wise-ness. Build up their integrity, don't tear it down. Most of the time, swearing is trying to grab attention or otherwise control things around us with words in a way words aren't meant to do.
Meaning matters. With some words, regardless of your intent, the effect of your word on your listeners, and on you, is an unhelpful one. Every time you say [sounds like fit] you're going the opposite direction of Philippians 4:8. Every time you say the f-word or even its milder synonyms, you are demeaning the sexual act, no matter what the context or your intent are. Under this point, I also reject substitute swear words like gosh and darn. They refer to God and damn. We use them to express amazement, wonder or frustration, when we aren't really thinking deliberately about God or hell. It's a form of taking God's name in vain.
Discretion is the Biblical example. It often refers to private body parts for example, but uses euphemisms to keep from crassness. See the Ezekiel example above, and 1 Thessalonians 4:4, and consider the swear words that could have been used! (Well, maybe just don't bring them to mind...) Many Christians who want to excuse their crass speech by appealing to biblical example ignore this. You won't find the f word in the Song of Solomon. Philippians 3:8 is another example where it is insisted Paul says the word for excrement that rhymes with "fit." Not necessarily. The word could mean anything from "junk" or "trash" to that word, and translators aren't twisting the word to use a milder synonym like "rubbish." Even when referring to crass or indiscrete things, the Bible does so discretely.
Prudishness? One can be Biblically discrete without being prudish. The difference is two-fold. Are you offended that Scripture would speak of such things, or in that way? That's the problem of the prude. Or, second, how wound up you make yourself for others' sake over a minor thing? Condemnation and huffy offense are the prude's way. When my friends swear, I don't make a big to-do. But neither am I going to follow their example. I will often respond by using a euphemism for what they said as soon as I can, to subtly make the point that I'm not going to talk that way, but can talk about the same things. But I'm not going to disrupt a conversation for it, either, unless it gets really frequent or severe.
Being macho. In some circles that advocate a masculine Christianity you find more swearing among the men. There is a whole culture I'm fighting here, where a gentleman may mildly swear when ladies are not present, to accent the gender distinction and show that "we can be men here." I'd find it laughable if not so sadly misguided from Scripture. Ephesians 5:3-4 is no less true in a group of men than anywhere else. Yes, social norms adjust a bit based on who we are with. I'll talk differently with people in their 20s than people in their 60s. But Scriptural principles always apply to everyone, and one of them is to avoid coarse jesting (Eph. 5:4).
Against the tide.
So swearing sucks. There, I just did it. I swore. Did you notice? Cultural usage of words changes over time. "Suck" used to get you into a fair bit of trouble, but today we hardly realize what we are saying, and you hear 7 year-olds saying it. Remember what this used to refer to?! Still does, I'd say, so I don't say this word in that context, and I'm teaching my kids not to say it. "Stinks" is just fine for a substitute.
Appeals to justified swearing are almost always hollow. If you think you won't be heard without your strong language, you are either insecure or fearful, or too desperate to be heard or understood. Speech seasoned with salt does NOT mean salty sailor talk, but truth with taste. Teens, don't think you have to swear to prove to yourself or your friends that you are growing up. Call your friends out on their unhelpful speech. Ask them to help you keep your mind out of the gutter. Parents, teach your children from a young age to be careful what they say. We will be judged for every idle word.
Doug Wilson writes quite helpfully about this topic here.