Leonard: Sheldon, this date is probably my one chance with Penny. What happens if I blow it?
Sheldon: Well, if we accept your premise, and also accept the highly improbable assumption that Penny is the only woman in the world for you, then we can logically conclude that the result of blowing it would be that you end up a lonely, bitter old man with no progeny. The image of any number of evil lighthouse keepers from Scooby-Doo cartoons comes to mind.

Sheldon: I don't understand your objection, Professor Goldfarb. Why wouldn't the Sonora Desert make a perfectly good Promised Land?
Goldfarb: Go away!
Sheldon: We could call it Nuevo Jerusalem.
Goldfarb: Please go away!
Sheldon: Said Pharaoh to Moses!

Girl: What are you?
Sheldon: I'm gonna give you a hand: weawww.
Girl: A Choo choo train?
Sheldon: Close! weawwww
Girl: A brain damaged choo choo train?

*Leonard tries to slip a note under Penny's apartment door*
Penny: Hi.
Leonard: Oh.
Penny: What's going on?
Leonard: Um, here's the thing. (Reads from the note.) Penny, just as Oppenheimer came to regret his contributions to the first atomic bomb, so too I regret my participation in what was, at the very least, an error in judgment. The hallmark of the great human experiment is the willingness to recognize one's mistakes. Some mistakes, such as Madame Curie's discovery of Radium turned out to have great scientific potential even though she would later die a slow, painful death from radiation poisoning. Another example, from the field of Ebola research-
Penny: Leonard.
Leonard: Yeah.
Penny: (hugs him) We're okay.

Leslie: Just so we're clear, you understand that me hanging back to practise with you is a pretext for letting you know that I'm sexually available.
Leonard: Really?
Leslie: Yeah, I'm good to go.
Leonard: I thought you weren't interested in me.
Leslie: That was before I saw you handling that beautiful piece of wood between your legs.
Leonard: You mean my cello?
Leslie: No, I mean the obvious crude double entendre. I'm seducing you.

Howard: When they perfect human cloning, I'm gonna order 12 of those.

Sheldon: (On the phone) This is Dr. Sheldon Cooper. Yeah, I need to cancel my membership to the planetarium. Yeah, well, I'm sorry too, but there's just no room for you in my wallet. No, I understand, but it was between you and the Museum of Natural History, and frankly, you don't have dinosaurs. Oh, I'll miss you too. Bye-bye.

Raj: What just happened?
Leonard: Beats the hell outta me!
Howard: I'll tell you what happened, I just learned how to pick up Indian Chicks.

Leonard: If you don't like this Christy, why are you letting her stay?
Penny: Well, she was engaged to my cousin while she was sleeping with my brother, so she's kind of family.

Raj: Okay, if no one else will say it, I will. We really suck at paintball.

Leonard: I have 26 hundred comic books in there, I challenge you to find a single reference to Kryptonian skin cells.
Sheldon: Challenge accepted. (Tries to open the apartment door.) We're locked out.
Raj: Also, the pretty girl left.

Mary Cooper: Good morning, snickerdoodle. Well that looks awful fancy, what is that?
Sheldon: It's my idea of what DNA would look like in a silicon-based life-form.
Mary Cooper: But intelligently designed by a creator, right?

Leonard: Sure, if he wants to spend years doing her homework while she drinks herself into a stupor with non-fat White Russians and you're the one holding her head while she's puking and telling you she wishes more guys were like you. And then she gets into Cornell, because you wrote her essay for her and you drive up to visit her one weekend and she acts like she doesn't even know you.

Leslie: PMS? It's a couple of days early, but
Leonard: No, it stands for Perpetual Motion Squad.
Leslie: Oh, right, of course, what was I thinking?

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.