Season 2, Episode 20 - The Hofstadter Isotope
Aired April 13, 2009
When Penny accompanies the guys to the comic book store, she is charmed by store owner Stuart and agrees to go on a date with him. Leonard wonders why Penny has fallen for a guy who is just as geeky as he is. In an effort to improve his love life, Leonard ventures out to Ladies' Night with Howard and Raj.