Arriving in Lorien and meeting Haldir and the other elves was a very… trying experience for Gimli. In the book, he’s pretty offended that they don’t trust him, but he just complains about his honor. In the Peter Jackson movies, Gimli actually shoots an insult at Haldir in response to his statement that they “have not had dealings with the dwarves since the Dark Days.” (Watch a short clip of the exchange here.) But Gimli’s insult remained a mystery to viewers for quite a while.
After the scripts were released, we knew that what Gimli said was “Ishkhaqwi ai durugnul.” But that’s not really all that helpful, since we still didn’t know what it meant - Tolkien wrote so little about Khuzdul, the dwarvish language, that any Khuzdul dialoge in the movies (with the exception of the battle cry “Baruk Khazâd! Khazâd ai-mênu!”) is actually Neo-Khuzdul, which is Khuzdul that has been constructed by modern linguists to fill in the blanks that Tolkien left in the language’s development. Basically, what this means is that the insult was “made up” by writers for the movie, and therefore isn’t based in any of Tolkien’s writings.
But, according to Andreas Fröhlich, who worked on the German translation of the movie, the insult means "I spit upon your grave." Which is pretty insulting, even if you aren’t dead yet. So, now we know.
SOURCES: “Tolkien’s Languages in the FotR Movie”