One of them wanted to have some fun, so said to the other - "I'll give you $100 if you take a big bite of that turd".
His colleague figured $100 was a good chunk of cash, so did the deed. Feeling thoroughly humiliated, he pocketed the $100 and they carried on.
Further down the street they came upon another turd.
The angry economist now wanted revenge so made the same proposal back to his colleague, who also agreed and took a bite of the turd, earning back his $100.
Later one of them said to the other "you know, I can't help but feel we both ate shit for no reason."
His collegue replied "what do you mean? We raised the national GDP by $200."