Noun
The trigger finger of a person eager to fire their weapon or likely to do so unexpectedly.
(idiomatic) The metaphorical trigger finger of a person with a tendency or readiness to act in haste or without consideration; a tendency to so act.
Given any remote chance to gun down an effective spokesman for conservative economics as a secret fascist and torturer, even Nobel laureates can, we see, succumb to an itchy trigger finger.