The Big Bang TheorySeries 2 Episode 20: The Hofstadter Isotope
Leonard is devastated when the geeky sales clerk in a comic book store hits on Penny. Even worse, she doesn't mind! Leonard can't believe that Penny would date one of `them', unless it is him. Sheldon tries to scupper the budding romance by constantly challenging the clerk to engage in dialogue from Batman.
- Original air date