A man that will have sex with anything that has a hole. Not to be confused with a man-whore, a monster has no preference and will give himself up to anyone or anything. Where as a man-whore, sleeps with many people, but often has preferences and is actually attracted to the person they are persuring.
Boy 1: I wanna get some of dese girls home tonight.
Boy 2: Fo real. Dere's one rite dere.
Boy 1: Yo! Dat girl is HIT! I would NEVER tap dat!
Boy 2: I dun care man, pussy is pussy!
Boy 1 is clearly a man-whore but Boy 2 is a Monster.