Leonard: Girls like Penny never end up with guys who own time machines.
Sheldon: I disagree. Your inability to successfully woo Penny long predates your acquisition of the time machine. That failure clearly stands on its own.
Leonard: Thanks for pointing it out.
Sheldon: In addition, your premise is flawed. In the original film, Rod Taylor got Yvette Mimieux with that very time machine. In Back to the Future, Marty McFly got the opportunity to hook up with his extremely attractive young mother.
Leonard: Those are movies.
Sheldon: Of course they're movies. Were you expecting me to come up with an example involving a real-life time machine? That's absurd

Sheldon: Are you upset about something?
Leonard: What was your first clue?
Sheldon: Well, it was a number of things: first, the late hour; then your demeanor seems very low energy; plus your irritability...
Leonard: Yes, I'm upset!
Sheldon: Huh, I don't usually pick up on those things. Good for me.
Leonard: Yeah, good for you.
Sheldon: Oh, wait, did you want to talk about it?
Leonard: I don't know, maybe.
Sheldon: Wow, I'm on fire tonight

Sheldon: I propose we add "pants must be worn at all times in the time machine"
Leonard: Seconded.
Wolowitz: I was gonna put down a towel

Leonard [about the time machine]: The lights flash, and the dish spins. You wanna try it?
Penny: No, I don't wanna try it! My God, you are grown men! How could you waste your lives with these stupid toys and costumes, and comic books, and-and... now that-that...
Sheldon: Again—time machine.
Penny: Oh, please, that's not a time machine. If anything, it looks like something Elton John would drive through the Everglades

Leonard: So, how do you two know each other?
Missy: He once spent nine months with my legs wrapped around his head.
Leonard: Excuse me?
Sheldon: She's my twin sister. She thinks she's funny, but frankly, I've never been able to see it.
Missy: That's because you have no measurable sense of humor, Shelly.
Sheldon: How exactly would one measure a sense of humor? A "humormometer?"

Wolowitz: Okay, you two have to back off.
Raj: Why should I back off? You back off, dude.
Leonard: Excuse me, this is my apartment, and she's my roommate's sister.
Howard: So what? You've already got Penny.
Leonard: How do I have Penny? In what universe do I have Penny?
Wolowitz: So, I can have Penny?
Leonard: Hell, no!

Leonard: How did you know my birthday's Saturday?
Penny: I did your horoscope, remember? I was going to do everybody's until Sheldon went on one of his typical psychotic rants.
Sheldon: For the record, that psychotic rant was a concise summation of the research of Bertram Forer, who, in 1948, proved conclusively through meticulously designed experiments that astrology is nothing but pseudoscientific hokum.
Penny: Blah, blah, a typical Taurus

Leonard: I don't celebrate my birthday.
Penny: Shut up. Yeah, you do.
Leonard: It's no big deal. It's just the way I was raised. My parents focused on celebrating achievements and being expelled from a birth canal was not considered one of them

Leonard: I'm her friend, I'm not going to take advantage of her vulnerability.
Wolowitz: Wait, so you're saying that if in the depths of despair she throws herself at you and demands you take her right there, right now, you'll just walk away?
Leonard: I said I'm her friend, not her gay friend

Penny: Maybe we should talk first.
Leonard: Okay, but before you say anything, have you ever heard of Schrödinger's cat?
Penny: Actually, I've heard far too much about Schrödinger's cat.
Leonard: Good.
[Leonard kisses Penny]
Penny: Alright, the cat's alive. Let's go to dinner

Leonard: Now that I'm actually about to go out with Penny, I'm not excited, I'm nauseous.
Sheldon: Then your meal choice is appropriate. Starch absorbs fluid which reduces the amount of vomit available for violent expulsion

Leonard: At least I didn't have to invent 26 dimensions just to make the math come out.
Sheldon: I didn't invent them, they are there!
Leonard: In what universe?
Sheldon: In all of them, that's the point

TBBT Quotes

Oh, Bernadette, please play my clarinet.

Raj's poem

Sheldon: I'll have a diet Coke.
Penny: Can you please order a cocktail? I need to practice mixing drinks.
Sheldon: Fine... I'll have a virgin Cuba Libre.
Penny: That's... rum and Coke without the rum.
Sheldon: Yes, and would you make it diet?