This meme comes from the computer RTS game, Dawn of War. The particular expansion is Soulstorm. Soulstorm is the third expansion. During one part, a Chaos Lord, one of your enemies, sees your troops, and you, coming in these tanks, which are called Rhinos. He proclaims the Rhinos to be little metal boxes, calls you a coward, a fool, and then gives a speech about how he will take away your "little metal boxes." There are no variations on this meme. It is notable for its randomness, and its applicability to anything, from tanks to laptops to buildings.