"The Financial Permeability"

Sheldon lends Penny some money which makes Leonard go and try and collect some money from her ex-boyfriend Kurt for her.

"The Friendship Algorithm"

In order to get time on the super computer at work that he needs for his experiment, Sheldon must befriend Kripke who is in charge of the device.

"The Killer Robot Instability"

When Penny's comments about Wolowitz's love life sends him into depression, the boys are about to lose their most important teammate in an upcoming robot fighting competition.

"The Bath Item Gift Hypothesis"

It's Christmas time and Sheldon is annoying everyone with his theories on gift giving etiquette. Meanwhile, Leonard gets jealous when Penny stars dating one of his handsome co-workers.

"The Vartabedian Conundrum"

When Sheldon and Penny convince Leonard that Stephanie has moved in, Sheldon tries to slow the relationship down.

"The White Asparagus Triangulation"

Sheldon tries to secure Leonard's relationship with Stephanie and sets up a scenario where Leonard can prove he's the alpha male.

"The Lizard-Spock Expansion"

Wolowitz thinks he's found his soul mate, Dr. Stephanie Barnett (Sara Rue), until she meets Leonard. Wolowitz lets Stephanie drive the Mars rover, which gets stuck in a ditch.

"The Panty Piñata Polarization"

When Penny's cable goes out, she starts going over the guys' apartment to watch America's Next Top Model. However, after violating some of Sheldon's arbitrary rules, he bands her from coming over.

"The Cooper-Nowitzki Theorem"

After an open house night at the University with grad students, an obsessive student Ramona Nowitzki (Riki Lindhome) likes Sheldon and makes her way into becoming his girlfriend / assistant.

"The Euclid Alternative"

When Leonard needs to work the graveyard timeslot to gain access to the lasers for his experiment, Sheldon loses his ride to the university.

TBBT Quotes

Mrs. Cooper: Shelly! I'm so glad you're here!
Sheldon: I saw you having naked sex.

Penny: I give up, he's impossible
Sheldon: I can't be impossible, I exist. I believe what you meant to say is, "I give up, he's improbable."