A good place to kill an enemy within two seconds of kicking open a door is when you kick open your very first door in the game -- in "The Home Fires Burn" (second story mission). Keep some enemies alive before kicking open the door to the Baka mini-boss. You cannot kill Baka -- so it does not work on him. After kicking open the door, turn around and shoot one of his goons. This is best done with a rifle or shotgun. Note: There are limited opportunities to do this throughout the story. If you miss this opportunity, it is recommended you try this during a new game.