A couple of language-related links of possible interest:
The first one is Strong Language: A Sweary Blog about Swearing. I’ve said before than profanity and obscenity have a grammar of their own, and if you’re not fluent in the vulgar tongue you shouldn’t try to fake it – either do your research or leave it alone. As for invented bad language, the kind that’s sometimes found in (usually not very good) fantasy or science fiction, let’s just say that it tends not to work very well. If a writer doesn’t know how to swear in plain modern English, they’re not likely to be able to transpose that music to another key, either.
But if you’re minded to do the research – or if, like me, you’re a certified member of the word nut tribe – blogs like the one above are a good (and entertaining) place to start.
Another entertaining blog for the word nuts among us is Not One-Off Britishisms, a blog concentrating on bits of British slang and idiom that have migrated across the Atlantic into American English. (Not surprisingly, this blog also features profanity and obscenity from time to time, as in this post from 2012, where the blogger and commenters discuss the differing reactions on either side of the Atlantic to Loki’s insulting words to the Black Widow in The Avengers.)