This is a very good topic, Mycernius. I had thought of starting one like this myself, but hesitated due to my general lack of expletive vocabulary in its many, varied, interesting possibilities. I'd like to leave two remarks/questions here for a starter.
1. How is fluency in the pejorative subset of the language related to higher fluency in the language in general ?
I've held off using cuss words, phrases, and fixed expressions in my mother tongue Korean for about 25 yrs, and felt unable to express myself in so many instances. When I decided to change that, and began to speak out on my negative feelings (sometimes positive feelings, too), I felt such a release from the old tension that crippled my person. I am elated when I can deliver a full round of expletive ammo in polished style. I can feel whole as a person, and the language is now closer to what I consider full fluency.
2. Can cussing be considered a language universal ?
When I asked certain language questions of a Chinese conversation partner, a native speaker of Mandarin, she said that she was amazed how quickly many learners of Mandarin picked up that part of the language. Aside from being humorous, this suggests that cuss words constitute a core area in the innate language ability of all humans. I wonder if anyone can prove this in general. Let me have a shot at it.
All cultures have ways of expressing negative emotions which is reflected in the language(s). When a non-native speaker of English comes in contact with English for the first time, the usually short and nonamibivalent character of the cussing expressions are some of the easiest examples of English to assimilate.
It is a very good thing that this mode of speech is available to the language learner, both for the emotional well being and for the practice of phonology, morphology, and syntax in the newly aquired language.