The Jargon File (version 4.4.7, 29 Dec 2003):
clue-by-four
[Usenet: portmanteau, clue + two-by-four] The notional stick with which one
whacks an aggressively clueless person. This term derives from a western
American folk saying about training a mule ?First, you got to hit him with
a two-by-four. That's to get his attention.? The clue-by-four is a close
relative of the LART. Syn. clue stick. This metaphor is commonly
elaborated; your editor once heard a hacker say ?I smite you with the great
sword Cluebringer!?