from
Jargon File (4.4.4, 14 Aug 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!"