The origional source of this word has become forgotten (mainly due to excessive alcohol consumption) however what we are sure of is it's meaning. The term refers to a child who goes by the name of Anthony Greensmith. As you can imagine, describing him as a top class, straight up, grade A, class act, useless moron puts a large amount of strain on ones larynx, so a word was needed to allow a short sharp delivery, as opposed to a long babbling tirade. Using our immense wit and tact, we replaced the beginning of the childs name with the term Goon.
Anthony: "Hi, I'm Barry Scott. Bang, and the dirt is gone!"
Girl: "Get the fuck away from me"
Everyone: Haha, nice work Goonsmith