Adjective

1. Having a tendency or desire to shoot a firearm irresponsibly before adequately identifying the target.

   The bystanders were indiscriminately gunned down by trigger-happy gang members.

2. Inclined to behave recklessly, especially with machinery.

   Be careful when you work near him; he's trigger-happy with that chain-saw.

3. Inclined to react excessively or violently at the slightest provocation.

   He was so trigger-happy that he wheeled and punched me when I brushed by him in the hall.