The Big Bang Theory: Season 4, Episode 9

4 - 9: The Boyfriend Complexity

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