As an aspiring wordsmith, I decided to make a small guide on how to create slang, profanity, and other neologisms (that’s a fancy way of saying “made up words”) that don’t sound… well, dumb.
First: it needs to roll off the tongue. If it’s slang, and a swear especially, you want to be able to say it with little obstruction. Many English slangs or swears are short, mono- or duo-syllabic, and snappy. For instance: zounds (God’s wounds), berk (Berkshire Hunt, rhymes with a rude word for female genitalia), etc. If it isn’t compact, it must roll off the tongue in some other way. Many Roman swears were highly technical, but rolled off the tongue almost poetically, such as “pedicabo ego vos irrumabo” (I will violate your anus and throat).
Second: etymology! Where does your swear word or slang come from, and how can you trace it back to its roots? Maybe it’s an evolution or corruption of a previous swear. Maybe it evolved as a way to avoid a ruder word, and took on a life of its own (the origin of many military swear words). If it’s a swear word especially, it’s often pejorative, and rooted in some insult to the subject. Most modern swear words, for instance, are rooted in sexual or religious language.
Let’s give an example. A sapient avian species has a slang word for genitals, cloc (derived from “cloaca” and pronounced like “cloak”). However, it can also be applied pejoratively to an individual: said avian species likely has a seasonal sex drive, and thus might see mating more as a chore that needs to be done every so often. So when applied to a person, cloc takes on the context of being a busybody, or a nuisance.
Third: Introduce the word into your story before using it in a dramatic context. This allows us to become acclimated to the idea of the swear word having an appropriate means and use. And if we know of its existence and see that it makes sense within the context of the universe itself, that means it can actually be used to add impact to a scene instead of deflating it because the audiencs is busy wondering why you’re tossing around a nonsensical neologism out of the blue.