The plot of that Danish film, Idioterne (the Idiots), directed by Lars von Trier, was that a group of "normal" people living in a squat get their thrills by pretending to be mongs - taking it in turns for one of the group to be the minder. There's an orgy scene alright but there's no actual mongs in it I'm afraid
A group of perfectly intelligent young people decide to react to society's cult of an aimless, non-creative and non-responsible form of intelligence by living together in a community of "idiots". Their main activity becomes going out into the world of "normal" people and pretending to be mentally retarded. They take advantage of this situation to create anarchy everywhere they go and try by every possible means to make people annoyed, disturbed, miserable, ridiculous, angered, and shocked. The films start as they recruit a new lost soul and introduced her to their megalomaniac leader.