D'Arvit is the most commonly used Gnommish word in the Artemis Fowl series. We know it's a swear word from the first time it's introduced:
“D’Arvit!” growled Root. (There is no point translating that word as it would have to be censored.)
-- Artemis Fowl, Chapter 5: Missing in Action (emphasis mine)
And from one of the later books:
“Hurkk,” said Artemis half-choking with surprise.
“D’Arvit,” swore Holly.
“I think we all know what D’Arvit means,” said No.1. “But hurkk is not English.
-- AF and the Time Paradox, Chapter 5: I Now Pronounce You (emphasis mine)
Is the actual meaning of the word D'Arvit ever revealed or implied? Perhaps some hints are dropped from which its general ballpark can be deduced (e.g. is it sexual? does it refer to bodily waste?) Or perhaps Colfer has said something about this in an interview?