The Boyfriend Complexity

The Boyfriend Complexity is the ninth episode of the fourth season of The Big Bang Theory.

Plot Summary
Penny asks Leonard to lie to her visiting father (Keith Carradine), while Howard, Raj, and Bernadette spend the entire night looking through a telescope.

Expanded Plot
Leonard is flattered when he shows up at Penny's door and gets a kiss from Penny. Later, Penny informs him that her critical father Wyatt (Keith Carradine) is visiting, and she asks him to pretend that they're back together because he's the only boyfriend she's ever had that her father likes. Leonard is initially wary of the idea, but gleefully plays along to get Penny to confess (he also calls her on her hypocrisy at being mad at him for going along with her stupid, flawed plan), which she finally does while her father and Leonard are Wii fishing. Penny's father confronts her about the hoax; then, after Penny leaves the room, he begs Leonard to get back together with Penny because he wants grandchildren who don't grow up in a house with wheels and knows Penny's next boyfriend(s) won't provide them. Leonard plays along as Wyatt pretends to angrily throw him out of the apartment.

Meanwhile, Howard and Raj spend the night in a control room for a ground-based telescope operating in Hawaii, hoping to find the star Epsilon Eridani dim, which would be evidence of a planet orbiting it. Raj gets mad at Howard when he discovers that Howard invited his girlfriend Bernadette until he discovers that Bernadette brought wine. When an intoxicated Raj complains that "no girl ever wants to kiss him," Bernadette shows sympathy for him and he attempts to kiss her. Howard attempts to stop Raj but they end up sharing a lengthy kiss. The following morning, when asked by Leonard and Sheldon, both act awkward around each other.

Trivia

 * The title refers to Leonard pretending to be Penny's boyfriend to please her father.
 * Penny's father's name is changed from Season 2's "The Maternal Capacitance" when Penny referred to him as "Bob," however in this episode his name is Wyatt, implying "Bob", was just a nickname.