Definition from Wiktionary, the free dictionary
- (idiomatic) To raise a false alarm; to constantly warn others about an imagined threat, thereby failing to get assistance when a real threat appears.
- The politicians would cry wolf at the slightest provocation so when the real threat appeared no one believed them.
See also 
raise a false alarm
- 1907, H. G. Wells, The War in the Air, chapter II, section 4
- The newspaper placards that had cried "wolf!" so often, cried "wolf!" now in vain.
- 1919, H. L. Mencken, The American Language, chapter 5
- ...and the critical sense of the professors counts for little, for they cry wolf too often...
- 1983, Ronald Reagan, Presidential Radio Address - 15 October, 1983
- ...those who created the worst economic mess in postwar history should be the last people crying wolf 1,000 days into this administration...