You have two cows...

From wikibooks:

"You have two cows" is the beginning phrase for a series of political joke definitions. "You have two cows" jokes originated as a parody of typical "Economics 101" examples featuring a farmer in a moneyless society, using his cattle and produce to trade with his neighbors. The examples ran along the lines of "You have two cows; you want chickens; you set out to find another farmer who has chickens and wants a cow, etc." They were meant to show the limitations of the barter system, leading to the eventual introduction of currency and money. The "two cows" parodies however, place the cow-owner in a fully-fledged economic system where cows are used as a metaphor for all currency, capital, means of production, etc. The intent is often to point out flaws and absurdities in those systems.

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Uncyclopedia also has an entry.