I used to have an absolutely foul mouth. Working in customer service will do that to ya if you aren’t careful–one gets so incredibly frustrated with customers/coworkers/insane corporate situations or expectations, and with coworkers all around you using that sort of language in the breakroom et all…well, you get the idea.
However, I realized it had become an issue when I found myself automatically using that kind of language in most conversations, and not just in insane breakroom rants about moronic or nasty customers.
As I understand it, “bad language”, per se, is different from blasphemy. Blasphemy is a far more serious sin.
How did I break myself of the habit? 'Twasn’t easy. I ended up substituting rhetoric, some Monty Python quotes (“Get me the Holy Hand Grenade of Antioch!”) and the occasional rude comment in another language. (I once knew a choir director who, when beset by a distinctly peculiar congregation on the one hand and a choir full of Strong Minded Women on another, would swear fluently in Lithuanian at the organ, but that’s another story.) I wish I were a more charitable person than I am–I’m working on it, but it’s a nasty struggle–but for now I’ll accept that I not teach small children words that their parents would rather not define quite yet. I still find myself biting my tongue on occasion, but it’s gotten better.
For your situation, I’d recommend a few things, depending on what kind of language we’re talking about:
- If it’s blasphemy, it isn’t okay, EVER. Period, full stop, end of statement. I used to use it. As I broke myself of the habit, a word would occasionally slip out, at which point I’d immediately stop and apologize to Our Lord. Might sound hokey, but it works, if only because it’s embarrassing to say “Sorry, Lord” out loud.
- If it’s “dirty” language, particularly a word generally used to denote excrement, I’d roll my eyes and ask if she couldn’t find something a bit more original. I mean, really? It’s the adult equivalent of a three-year-old calling something he doesn’t like “poopy”, and it’s just as juvenile. For that matter, “poopy” has more syllables.

- If it’s sexual language, even if not meant sexually (see the word which usually indicates copulation, and words referencing male or female genitalia), I’d ask her (as a previous poster suggested) to look up the precise etymology of the word, and then have a TOTB-centered chat about why such language is disrespectful about the pretty glorious thing that is human sexuality. The phrase “**** you” is particularly nasty because of what it really means: “may you have this ‘embrace’ with no love in it.” Not good, not good at all. As for the words indicating genitalia, I, as a different previous poster suggested, would explain that they’re not cute, amusing, or attractive and, in addition, that they’re pretty disrespectful to God because He created those organs to give us the power to create new life, and by using those words like that we’re saying that those organs which are to be respected over others are the opposite of that. No, not appropriate. Words have meaning.