Profanity doesn't really exist in Lojban, at least not the same way it does in other languages. This is because words that have become considered "bad words" in other languages have mainly arisen by accident or out of existing, non-offensive words. Lojban, however, was designed for functionality and to reduce the need for evolution, so there hasn't been much need for creation of profanity terms. Moreover, the speaker mass of Lojban is largely concentrated on the Internet, not in verbal, face-to-face confrontations, and due to the educational and collaborative nature of most Lojban sites and channels, the amount of flaming going on is negligible.

However, that which follows is, to the best of my knowledge, the most appropriate (no pun intended) way to swear in Lojban.

Disclaimer: Many Lojban sites and channels discourage or prohibit the use of profanity, English or otherwise. Use the same discretion when cursing in Lojban as you would in any other language.

Addressing someone in preparation for cussing them out

The primary way to address someone in Lojban is by using "doi" followed by the recipient's name. A somewhat rougher and louder version is to use "ju'i" instead of "doi". After using one of these particles, you may opt to either address the recipient with a curse word or two, rationalizing that that is what they are and you can address them as such, or to simply address them with their name and then tell them what they are.

You may also make use of "do po'u" to start a phrase meaning "You bastard, bitch, etc." The cmavo "po'u" roughly translates to "the", as in "Sonic the Hedgehog".

Attitudinals

You may find that attitudinals are often useful for preceding statements, such as ".o'onai"/anger ("You asshole!"), ".i'enai"/disapproval ("That bitch needs to get her priorities straight."), or ".a'ucu'i"/disinterest ("Fuck this shit.") More can be found in the article Nonviolent Communication with Lojban attitudinals.

Profanity for people

Racial slurs

These are usually thought of as bad form, even among people who are already cursing, but you can simply use one of the ethno-cultural terms found in the gismu list.

Others

Varieties on the F-word

• Nora fucked Joey.
  • la noras. pu gletu la jo'is.
• Fuck this shit. I'm leaving.
  • .a'ucu'i le tcini se mabla zo'e .i mi ba cliva ti
• What the fuck?
  • .ianai mi na jimpe
• Fuck you.
  • .i'anai ko se gletu
• Where are my fucking keys?
  • le mi ckiku poi se mabla cu zvati mo