CBS

Season 1: Episode 6 - The Middle Earth Paradigm

The Middle Earth Paradigm: The guys go to Penny's Halloween party. Leonard ends up getting humiliated by Penny's hunky ex-boyfriend while Sheldon, Wolowitz and Koothrappali try desperately to make a mark on the social scene but with limited success. After the party, Penny is a little drunk and sad after seeing her ex and ends up kissing Leonard.