Rent

Penny is heard singing and Leoandard and sheldon run away and penny runs into them inviting them to come and see her show of the workshop profucion of rent

Background

It was a one night show and Penny thought there would be a lot of casting agents. Leonard lies to Penny to get out of it

Trivia
The song Penny was singing was called "Out Tonight " a song in the musical Rent.

The lie could be uncovered by If she were to log on to www.socalphysicsgroup.org/activities/other, click on upcoming events, scroll down to seminars, download the pdf schedule, and look for the seminar on molecular positronium, well then, bippidy-boppidy-boo, our pants are metaphorically on fire.