Leonard: Should we go bring him back?
Penny: Well, you're the one worried having someone live with us is a sign of problems.
Leonard: Oh, that was just because my mother got in my head. It's like being possessed, but instead of Satan, it's -- Actually, it's the same thing.

Leonard: What would you be if you were attached to another object by an inclined plane, wrapped helically around an axis?
Sheldon: Screwed?
Leonard: There you go.

Leonard: Penny. We are made of particles that have existed since the moment the universe began. I like to think those atoms traveled fourteen billion years through time and space to create us, so that we could be together and make each other whole.

Sheldon: This song is never going to stop. Have you ever dealt with something so relentlessly irritating?
Leonard: That's a trick question, right?

Sheldon: Well, I think it's very nice that you're helping out our friend.
Leonard: I think it's nice that you're taking whatever medication Amy's clearly giving you.

Amy: This isn't about me and Sheldon. This is about Rajesh moving in with Leonard and Penny.
Beverly Hofstadter: Interesting. They've found a need to take yet another roommate. Seems they're avoiding some harsh realities themselves.
Sheldon: I had no idea all our relationships were such a disaster. Boy, you're good.
Beverly Hofstadter: That is the word on the street, dear.

Raj: Maybe moving in was a bad idea. I haven't been here one day, I'm already causing problems.
Penny: You didn't do anything. It's Sheldon.
Leonard: "You didn't do anything.It's Sheldon." That'd make a nice needlepoint pillow.