Sheldon: You know, this might sound far-fetched, but I'm on the market now. If I dated Mandy, that would teach both Leonard and Amy a lesson.
Penny: That's ridiculous.
Sheldon: Oh, you're right. I could never be with a woman whose self-esteem is so low she could be with Leonard.
Penny: I'm with Leonard.
Sheldon: Yeah, I know. Forever.