The Big Bang Theory Season 1 Episode 10
The Loobenfeld Decay
When Penny is given a part in Rent, the boys try to avoid to see her show after hearing her sing "Out Tonight" out of key in order to not hurt her feelings. Leonard makes up a lie that Sheldon feels is too transparent. Sheldon instead makes up a lie about a non-existent drug addicted cousin Leo who is in the need of an intervention. Sheldon then hires a fellow physicist to doubled majored in theater to act the part of his cousin. In the end, Leonard is stuck watching a tape of the performance so it was all for nothing.