Go to the Backyard Battleground
Go to your Multiplayer Portal
Choose Private Play
Choose Team Deathmatch on any map and difficulty
Choose Team Setup, scroll zombie team to Zombies : Z7 Invasion (all the zombies will be Z7 imps)
Choose Crazy Settings, Ridiculously Low Health (all characters will have 1 health).
Pick a character that shoots fast, trophy will pop on the first kill and the game will be over fast
(this will also pop the VIP's Only trophy)