Howard: Okay, you two have to back off.
Raj: Why should I back off? You back off, dude.
Leonard: Excuse me, this is my apartment, and she's my roommate's sister.
Howard: So what? You've already got Penny.
Leonard: How do I have Penny? In what universe do I have Penny?
Howard: So, I can have Penny?
Leonard: Hell, no!