"Whippersnapper" is a somewhat archaic term, rarely heard today outside of movies, and then usually from the mouth of a character portrayed as chronologically-challenged and hopelessly old-fashioned to boot. A "whippersnapper" is an impertinent young person, usually a young man, whose lack of proper respect for the older generation is matched only by his laziness and lack of motivation to better himself.
One might imagine that the term derives from the understandable temptation among more productive citizens to "snap a whip" at such sullen layabouts, but the whips in question actually belonged to the whippersnappers themselves. Such ne'er-do-wells were originally known as "whip snappers" in the 17th century, after their habit of standing around on street corners all day, idly snapping whips to pass the time. The term was been based on the already-existing phrase, "snipper-snapper," also meaning a worthless young man, but in any case, "whip snapper" became "whippersnapper" fairly rapidly.
Though "whippersnapper" originally referred to a young man with no visible ambition, the term has changed somewhat over the years, and today is more likely to be applied to a cheeky youngster with an excess of both ambition and impertinence.
And ain't it just perfect?!