When Sheldon learns that the neighbors above their apartment will move out, he begins to list all of the negative externalities that they didn't produce.

A new part of the Roommate Agreement includes payments for all of Penny's bad habits.

Howard and Sheldon feud over a parking spot.

Stringer Bell learns about product elasticity and then explains it to the gangsters he is in business with.

Harold, a tax auditor, visits Miss Pascal at her store to audit her because she paid only 78% of her taxes for the year. She gives him a hard time and states that she intentionally did not pay taxes for spending that she does not support. Miss Pascal mentions some ways that the government spends taxes.