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

Amy talks about tampons which upsets the guys.

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.

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.