Monster Closet: origin: Noun. Wolfenstein 3-D. but has also been found in later games such as Doom, Doom II, and the recent Doom III. Monster Closets are defined as being small chambers that monsters lurk in awaiting a victim to approach a certain vicinity or acquire a triggered object. Upon tripping said trigger, the wall (closest to the victim) of the Monster Closet is suddenly opened effectively causing the victim to wet his/her pants in terror and spray gunfire wildly in an attempt to erradicate said monster.
Person 1: "I totally hate the new Doom III game."
Person 2: "Why's that?"
Person 1: "Because it's full of monster closets that constantly make me have to change my underwear."