One of my favorite long-standing economics jokes (I have several favorites. What does that tell you about me?) is the use of cows to explain various concepts. As an example: "COMMUNISM: You have two cows. The state takes both and gives you some milk." There are a bunch of lists of these things - here's one of the more comprehensive ones (especially if you read the comments). My agricultural economist office-mate (and esteemed coauthor) even had this poster up in our office a few years ago.
My personal favorites? Malthusianism, Moral Hazard, and the Theory of the second best.
H/t Dad (who sent me this from his Hawaii vacation - now you see where I get it from).