coaster nazi: noun. a person who insists upon placing a coaster under your drink, no matter what. A coaster nazi will surreptitiously slip a small disk beneath someone's cup, glass, mug, stein, chalice, grail or beaker, unless the opportunity presents itself to "out" the offender in the loudest way possible and thereby introduce a parable in which the damage inflicted by excessive moisture upon a wooden surface leads to an environmental catastrophe that renders the Earth inhospitable to life.
Coaster nazis can usually be identified by a disproportionately high number of coasters relative to the number of horizontal surfaces in their homes that are large enough to support a drinking vessel of any type. Other signs include a tendency to secrete coasters (or in extreme cases, napkins) on their persons, or limited kleptomania, exhibited only in bars, and focused totally on those small cardboard coasters with beer brand logos on them.