"Laddybuck" is slang, and slightly insulting. A "lad" is a boy, and a "buck" is a young horse... so, laddybuck is "a young boy with bad manners, like an untrained horse."
"I'd pull yourself together, laddybuck," Wilson said very quietly. (Ernest Hemingway "The Short Happy Life of Francis Macomber")
An arrogant hillbilly in their late teens or early 20's. Also referred to as a half-raised hillbilly. One who thinks they know everything when in reality they don't know shit.