Commonly known as the male sex organ, or penis. It dates back to the classic 80's movie "better off dead". One character named "long duck dong" a foreign exchange student from japan boned a fat american teen with huge funbags.
LongDuckDong is a drink that some crazy drunk mexicans thought up one night in Kansas City when they were drinkin RedBull and GreyGoose vodka. When asked why they like the combination one simply said," because it makes my longduckdong!" hence the name!