The word "D'Arvit" in the Artemis Fowl series is the cuss word in Gnommish, used in dire situations by the protagonists. But the Urban Dictionary (which was used as a source for the answer to What does D'Arvit mean?, answering that the alleged Gaelic source below might be what is meant) claims (NSFW link!):
Despite popular belief D'arvit was not the creation of popular Irish author Eoin Colfer. In the Aran islands their is a legend that a dark banshee (Banshee which goes against the laws of magic) will rip your soul from your body when your alone regardless of whether your dieing or not and u feel a chill run up your spine a dark banshee is near and the only way to protect yourself would be to utter "Dh'ábhoit". The folklore was told all over the provinces of Connacht and Munster but during the English conquest by Henry the VIII. It was anglicized as "d'arvit".which is pronounced the same as the original and now its mainly used in Gaeltacht of Connacht as a form of a curse or cuss, in english or Gaelic (Irish).
Urban Dictionary is hardly a reliable source, true, but I can't seem to find anything either in support or refuting this.
Did Eoin Colfer coin the word or not? How accurate is the claim that it came from Gaelic?