Penny: Thanks. I just wanted to come by and wish you guys luck with your symposium.
Leonard: Oh, well, thank you.
Penny: You know, I got to tell you, a lot of friends would let their friend go alone, but that's not who you are. You are the kind of guy who stands by a friend when ... when he has a symposium to go to.
Leonard: I don't know what to say.

Sheldon: I've been doing some research on addiction, both the biochemical and behavioral aspects, and I think there's a problem with the current version of our lie.
Leonard: What are you talking about? It's fine. She bought it. It's over.
Sheldon: Sadly, it's not. Substance abuse is a lifelong struggle, but beyond that I have realized that the Leo I described would not have agreed to go to rehab.
Leonard: Why not?
Sheldon: Because Leo is a middle child.
Leonard: There is no Leo. How can you say that?
Sheldon: You didn't read the bio, did you? He's not just a middle child, he's the quintessential middle child, from a broken home to boot. Psychologically speaking, the attention he gets by rebelling even to the point of self-destruction is more emotionally valuable than the help he would get at rehab.
Leonard: I've got a solution.
Sheldon: Great, what is it?
Leonard: Get out.

Sheldon: I'm sorry, Leonard. This is Toby Loobenfeld. He's a research assistant in the particle physics lab, but he also minored in theater at MIT.
Toby: It was more of a double major actually. Theater and physics. You can guess which one my bourgeois parents pushed me towards.
Leonard: Yeah, I got it.

Penny: Hey, do you want to come over to my place, have coffee?
Leonard: Sounds good.
Penny: I have a video of me singing last night. Do you want to see it?
Leonard: Gee, why wouldn't I?
Penny: This is even better than you coming to the showcase, because now I get to watch you watch me.
Leonard: Yeah. Funny how things work out.

Leonard: A joke. Okay. How about this, um, okay, uh there's this farmer, and he has these chickens, but they won't lay any eggs. So, he calls a physicist to help. The physicist then does some calculations, and he says, um, I have a solution, but it only works with spherical chickens in a vacuum.

Leonard: Kandor was the Capital city of the planet, Krypton. It was miniaturized by Brainiac before Krypton exploded and then rescued by Superman.
Penny: Oh, nice!
Leonard: It's a lot cooler when girls aren't looking at it.

Penny: What is this?
Leonard: Oh, careful. That's my original series Battlestar Galactica flight suit.
Penny: Oh, why didn't you wear it on Halloween?
Leonard: Because it's not a costume, it's a flight suit.

Penny: So, you know, isn't there maybe some way you and Sheldon could compromise on this whole presentation thing.
Leonard: No. No. Scientists do not compromise. Our minds are trained to synthesize facts and come to inarguable conclusions. Not to mention, Sheldon is batcrap crazy.

Penny: I need some guinea pigs.
Sheldon: Okay, there's a lab animal supply company in Reseda you can try. But if your research is going to have human applications, may I suggest white mice? Their brain chemistry is far closer to ours.
Penny: I swear to God, Sheldon, one day I'm going to get the hang of talking to you.
Leonard: His mom's been saying that for years.

Penny: Ok, here you go Leonard. One tequila sunrise!
Leonard: Thank you! You know, this drink is a wonderful example of how liquids with different specific gravities interact in a cylindrical container!

Howard: So who wants to rent Fiddler?
Sheldon: No need. We have the special edition.
Leonard: Well, maybe we are like Haroun and Tanweer.

Leonard: Homo habilis discovering his opposable thumbs says what?
Kurt: What?

Penny: Why can't all guys be like you?
Leonard: Because if all guys were like me the human race couldn't survive.

Leonard: That's right, you saw what you saw. That's how we roll in the Shire!

Leonard: If he were any bigger, he'd have moons orbiting him.
Sheldon: Oh, snap.