turd in the punch bowl

n. A person who spoils a pleasant social situation. This metaphor is powered by a particularly vivid contrast: the inviting sensory appeal of a festive beverage juxtaposed with the revolting suggestion of feculent contagion. Therefore, labeling someone a turd in the punch bowl is most appropriate when the individual's deleterious influence goes beyond mere faux pas or nuisance behaviors, and rises to the level of deliberate offense for its own sake. Consider that the literal act of depositing or excreting fecal matter into a communal food-service container would be sabotage. The punch bowl and the feces connote certain additional nuances. The former is a symbol of public community, as such dispensers are frequently encountered at parties where they become a focal point for interaction. Freud famously identified feces with aggression and the possessive instinct. Thus a turd in the punch bowl suggests rage toward, and / or the urge to conquer, a community or society as a whole. Defecating into a punch bowl is a very public act, in contrast with poisoning the well or laying an upper decker, which are generally surreptitious. In particular then, to be a turd in the punch bowl is to be a willful and attention-seeking obstructor to the success of a social community.