A person who goofs off or fakes reasons not to do any work. U.S. military slang from approximately World War II, adapted from the use of the word "goldbrick" for an officer appointed directly out of civilian life. With no military experience, these men couldn't do anything; they were just civilians in uniform, bricks painted gold. (A brick painted gold was used by con artists in the late 1800s to swindle unwary buyers.)
Source: http://www.word-detective.com/090699.html