The Boy Who Cried Wolf
From Memory Alpha, the free Star Trek reference.
The Boy Who Cried Wolf is a Human fable about a young shepherd who enjoyed tricking the people of his village into believing that his sheep herd was being attacked by a wolf. When a real wolf appeared one day the boy called for help, but none of the villagers believed him. The wolf ate the boy and his sheep.
Q tried to ridicule Worf in 2366 by comparing his concern that he may not be trustworthy to "the story of 'The Boy Who Cried Worf". (TNG: "Deja Q")
Julian Bashir told Elim Garak the fable in 2371. While Bashir believed the moral to be that lying too much will cause people to never believe a person, Garak believed the moral was to not tell the same lie twice. (DS9: "Improbable Cause")
