trigger-happy

adjective2

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 or violently at the slightest provocation.

   • Be careful when you work near him; he's trigger-happy with that chain-saw.
   • He was so trigger-happy that he wheeled and punched me when I brushed by him in the hall.