Leonard: Look, just because we took our friend in does not mean that Penny and I are afraid to be alone.
Penny: Yeah, this is a special circumstance.
Beverly Hofstadter: Sheldon mentioned you tried to get your brother to live with you, as well.
Penny: Yeah, well, a circumstance can happen twice and still be special.

Leonard: If I take it off, Sheldon wins.
Penny: Sweetie, every night you don't kill him in his sleep, he wins.

Penny: I mean, who even reads Scientific American?
Leonard: It's kind of a big deal.
Penny: If it's such a big deal, how come the biggest celebrity they could get for the cover is a molecule?

Sheldon: Woman, you are playing with forces beyond your ken.
Penny: Yeah, well your Ken can kiss my Barbie.

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.