Lojban profanity is an issue that is overly debated and overly complicated. Instead of addressing the issue, the general consensus of the Lojban community has been to sweep the issue under the rug because "we're above that." However, I have been with enough people in this world to know that most people curse at least some time - intelligent people being no exception.
Obviously, saying something like "Oh crap!" is a lot different from saying something like "I'm going to f*ck your mom's f*cking sh*t filled c*nt you piece of sh*t *ssh*le," and indeed the more intelligent of this world would never resort to such vulgarity.
It is exactly this vulgarity which is simply unavailable in Lojban, as the words for sexual processes, sexual organs, and the progeny of various undesirables are all purely scientific and non-metaphorical. The word for anus in Lojban is ganxo, and has no connotation besides an organ which regulates the expulsion of feces. Likewise one could attempt to translate the word "asshole" into Lojban, but the question arises how to translate it? The ass part is easy, but is an anus really a hole? No, it's the end of the digestive tract. So should we call it the "ass type of ending of the digestive tract?" Maybe we could classify it as an opening? But it normally excretes, not intakes, at least according to its intended function.
Thus one can see the problem with bad words in Lojban: they haven't been formally created and it has been avoided to try and maintain Lojban's cultural neutrality, which essentially is starving it of any culture. Cross culturally however, there are certain things that will always be offensive, and the concept of dirty words and curse words is indeed common among mankind.