Hold the back button. Click on agent skills. Make firearm skill 1. Spawn a machine pistol. Spawn a few rubber ducks. They can be found in fun props. Then spawn a warden which is found under logistics AI. Shoot him a few times then throw a duck at him.
Another quick way to get it done, thanks Rista.
I had all agent skills on max and just picked up the duck and chucked it at the warden and he died in one hit.