I believe this is a very loose translation of the dictionary definitions for foolish talk, humorous old man.
Anyone a bit silly became a gaffer, and, ergo, some silly thing or act was gaff. Popped up in SE Mass around 1984.
Did you see that guy arguing for an hour over the lightsaber fights in Star Wars and how in Empire they cut through the railings, and in Jedi they didn't? What a gaffer! Have you ever see a thing called a Chick Tract? How utterly Gaff!
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