The Big Bang Theory Episodes :- The Codpiece Topology

In Season 2 Episode 2 Leonard feels hurt when he spots Penny with a new guy named Eric, after the guys come home from a Renaissance fair. To get back at Penny Leonard starts a relationship with fellow physicist Leslie Winkle, who along with the guys, makes fun of Leonard for being unable to sustain his relationship with Penny. Leslie finally starts dating Leonard, but assumes a dominating role till she tells Leonard to take on the male role. When Leonard convinces Sheldon to leave him and Leslie alone in the apartment, Sheldon confesses to Penny that he cannot stand Leonard’s relationship with his arch rival Leslie. Later Sheldon returns to the apartment and formally approves Leonard and Leslie’s relationship only to see them break up moments later due to a silly disagreement about physics and children.