Learning a language is a bit like being a child all over again.
Like most children, you go through a phase of being a potty mouth. Bad words hold glittering appeal, and all of a sudden you're learning NEW ones. *evil cackle*
I like them them for shock appeal.
But actually, it's a weird phenomenon. I find it very curious that the more a set of vocabulary becomes "illicit" or "naughty", the more appeal it holds. Same with slang words. They are much more interesting than regular grammar forms, and far more thrilling to use.
Some of the most interesting things I've learned so far have come from my phonetics professor. For instance, children between the ages of 0 and 7 can learn unlimited languages, because their ears do not have "filters", blocking out sounds. It is these same filters which block my ears from hearing the sound "ou" in "rouge" (my most dreaded word in the whole french language). Because I cannot hear it, I have incredible difficulty making it.
Other interesting facts include that children who are widely traveled and who learn different languages as small children, and thus are true "polyglots" have much smaller active vocabularies than someone my age (ancient, in language learning terms). They also have a tendency to be much less bigoted and harbor fewer cultural biases, having seen/accepted multiple cultures in action.
And now for one of the more hilarious stories of miscommunication between english speakers to date.
One of my friends was using naughty words (gros mots, in french, which means "fat words") and was rightfully called a potty mouth. However, to a native german speaker this sounds like "party mouse." So for the next few days she would say "party mouse" and do mouse ears with her hands whenever someone said a swear word.