There's a tradition of sorts in sci-fi where aliens or future humans use profanity that doesn't exist in the real world. I'm curious when this started. Which story or novel is the first time the writer made up profanity? It's acceptable if they used real profanity in addition to their made up profanity.
E E "Doc" Smiths Lensmen series (published between 1934 and 1948) included fictional profanity, at least in passing.
There's a scene where someone is transcribing a conversation in an alien tongue where one of the parties blanches at the use of an insult, the strongest in the language. In english it was something like "Shronizfied" with the meaning "descended from countless generations of muck living flatworm".
I'll dig the books out of storage and see if I can find an exact quote. [Nice to have a reason to re-read a classic ... ;-) ]
Anthony Burgess' A Clockwork Orange was written in 1962, and contained an entire lexicon of "Nadsat" slang. Some of those words are clearly intended as profanities.
Aldus Huxley's Brave New World predates that by quite a bit (1931), but I'd say its debatable whether the terminology in there really equates to profanity ("Gamma minus", a designation from the novel's caste system, is probably the closest thing to a profanity, although "soma", the name given to a fictional drug, is probably the most clearly "made-up" word).
There may very well be other examples, but these are the ones I could think of. While I think it's a great question, I'm not sure we'll get a real, definitive answer.
In Glory Road Robert Heinlein does actually discuss the use of profanity, and uses a word he considers profane.
That is the last word I am going to set down in a language that doesn't fit our alphabet. I had several more lessons, and won't mention them either, and from then on we spoke this lingo, except when I was forced to span gaps by asking in English. It is a language rich in profanity and in words for making love, and ricer than English in some technical subjects - but with surprising holes in it. There is no word for "lawyer" for example.
Courtesy of Google Book Search