Someone who is both prudish and square. Its immature sound is deliberate; it may very well be used by younger people, or people who act younger than they are.
It may be a generic insult as well; in other words, the person this is directed to doesn't necessarily need to be a prude nor a square.
British in origin.
"Stop being a prudy square, Neil, and do the shopping!"
October 26, 2004