fall off the cabbage truck

To be a nai¨ve newcomer. Imagine a flatbed farm wagon laden with fresh produce arriving in a city. Sliding off the back was a country bumpkin whose brain, or so smug sophisticated urbanites would agree, contained no more clue about worldly ways than a head of cabbage that might roll off the vehicle. A similar expression was to say that someone “just got off the boat,” a reference to immigration in the days of steamship passage when new arrivals were thoroughly ignorant of New World customs. Among the snappy denials to being called a hick or greenhorn were “I wasn't born yesterday” or “I might have been born at night, but not last night” or the wonderfully imaginative Midwestern comeback, “Hey, what makes you think I just got off the noon balloon from Rangoon?”