It’s important to be aware of your intended audience and modify some of the language you use as needed. However, it’s also important to be realistic and write the story that needs written, in the way it needs written, instead of freaking out because of what some people might think.
I made the conscious decision to expunge almost all of the strong language from my Atlantic City books, particularly the four-book prequel series. Even though it’s supposed to be a satire on modern-day preteens who think they’re so grown-up and such little bad-asses, there’s a limit. It makes me really uncomfortable to see so many F-bombs littered all over the pages (in the later books), and even certain salty words in the prequel series. I also felt it would be inappropriate for my target audience (mature upper MG) to read that many curse words.
In my straight historicals, I save the salty language for situations when it’s merited. For example, Lyuba drops the F-bomb every so often, but only when she’s extremely angry (like telling off her longtime antagonist Anastasiya or villain Boris). Kálmán also drops the F-bomb a few times, but it fits with his character. He’s been left so bitter and angry after surviving the Shoah, seeing so many friends dying, and losing his entire family.
Strong language loses its impact if it’s used carelessly, for no reason. If there are only five F-words in a 700-paged book, its usage shocks you, makes you stand up and pay attention, as opposed to seeing it 20 times every five pages (like Graham Nash’s autobiography).
Slang for body parts (as insults or anatomy terms)
Unless you’re writing erotica, this tends to turn me off. Even in erotica, using those words over and over again, or only one certain word, seems lazy and gross. I particularly hate the C-word, and refuse to use it. I used it in French a few times recently, but the word seems softer, less ugly, less misogynistic in another language. It also has a very strong impact, coming from a character who’s normally so sweet, loving, and seemingly naïve, but has been pushed to her breaking point and can’t contain all these repressed emotions anymore.
Please don’t show off how well you understand your characters’ native language or how much research you did into it. It’s better to sprinkle in meaningful untranslated words (e.g., insults, family relationships, terms of endearment, swear words, foods, words that don’t have a real translation), instead of gut-loading your book with them and forcing the reader to constantly flip back to the glossary.
As I’ve said many times before, a big reason I can read basic French fairly well is because I’ve read so many older books from the era when all educated people spoke French as a second language. Since these books had all these untranslated French dialogues and sentences, I had no choice but to read them with my now-106-year-old French dictionary by my side. I think I understand French better than Spanish, in spite of having studied Spanish for seven years!
Think of it as the difference between putting just the right mixture of spices on your food vs. dumping in three cups of salt or rosemary.
Don’t be afraid to have racist, anti-Semitic, anti-Catholic, etc., characters, if that’s truly what fits the story and that character. But even then, a little goes a long way. Perhaps mix up the terms your character uses, or don’t always use an epithet. We know, e.g., the protagonist’s parents are racists or that a character uses the N-word because that’s how everyone around him or her talks. Don’t hammer us over the head with it and constantly remind us of these attitudes.
I can count on one hand the number of times I’ve written the K-word as an adult. The slur “Yid” sounds so much softer and less harsher. That’s just a line I don’t like crossing.
The R-word is never acceptable. I’m blown away by how many people keep defending its usage, even after repeatedly being told it’s hurtful and offensive. I immediately lose respect for someone who uses that word as a synonym for stupid, foolish, frustrating, ridiculous, etc. Maybe a teenager honestly doesn’t know any better, but someone well into adulthood should know how to express oneself much more maturely and respectfully.
Some folks do take it too far, however. I honestly don’t see what the big deal is about expressions like “fallen on deaf ears,” “blind to the obvious,” “going crazy,” “quite mad,” and “a total lunatic.” Language evolves over time, and I think it’s fair to say the original meaning of words like crazy, moron, idiot, and mad has significantly evolved to the point where no one uses them in that way anymore. If you’re writing a contemporary, that shouldn’t be a worry.
Language that offends the overly-sensitive Tumblr crowd
These people are looking to get offended at every little thing. These are the navel-gazing SJWs whose minds are so open their brains fell out. I’m not going to kowtow to their arbitrary, constantly-changing whims and rewrite the entire English language or avoid using certain terms because the real world is a giant trigger warning for them.
Seriously, you can’t make this stuff up! Tumblrites are going to be in for such a shock once they enter the real world and discover things without 400 trigger warnings and a safe space attached.