Explain xkcd

Date: February 8th, 2011
From: Dan Hoey
Subject: Archimedes

sans-serif wrote:

  The joke is on how the first part of both sentence/proverb resembles
  common demands made by villains.

Yes!  And the cute thing is that the translation from the standard
"conditional" form to the threatening "imperative" form is the
substitution of "and" for "or", which makes this a symbolic logic
joke.