Sheldon: [about donating sperm] What if she winds up with a toddler who doesn't know if he should use an integral or a differential to solve the area under a curve?
Leonard: I'm sure she'll still love him.
Sheldon: I wouldn't.

Penny: I'm a Sagittarius, which probably tells you way more than you need to know...
Sheldon:Yes... it tells us that you participate in the mass cultural delusion that the sun's apparent position relative to arbitrarily defined constellations at the time of your birth somehow affects your personality.
Penny: Participate in the what?
Leonard: What he means is that wouldn't be his first guess.
Penny: Yeah, a lot of people think I'm a water sign.

[Discussing a large box of furniture which they have to take to the fourth floor, with the elevator out of order]
Leonard: Well, we'll just have to take it up ourselves.
Sheldon: I hardly think so.
Leonard: Why not?
Sheldon: Well, we don't have a dolly, or lifting belts, or any measurable upper body strength.
Leonard: We don't need strength, we're physicists. We are the intellectual descendants of Archimedes. Give me a lever and a fulcrum and I could lift the earth.
[The package starts falling on him]
Leonard: I don't have this! I don't have this! I DON'T HAVE THIS!
[Sheldon lifts the package off him]
Sheldon: Archimedes would be so proud.
Leonard: Well, do you have any ideas?
Sheldon: Yeah, but they all involve a Green Lantern and a power ring.

Leonard: [in Penny's apartment in the middle of the night] Do you realize if Penny wakes up, there's no reasonable explanation to why we are here?
Sheldon: I just gave you a reasonable explanation.
Leonard: No, you gave me an explanation. Its reasonableness will be determined by a jury of your peers!
Sheldon: Don't be ridiculous. I have no peers.

Leonard: Hello Leslie.
Leslie: Hi Leonard.
Leonard: I'd like to propose an experiment��
Leslie: Goggles, Leonard.
Leonard: Right. I would like to propose an experiment.
Leslie: Hang on. I'm trying to see how long it takes a 500-kilowatt oxygen iodine laser to heat up my Cup o' Noodles.
Leonard: I've done it. About two seconds, 2.6 for minestrone. Anyway, I was thinking more of a bio-social exploration with a neuro-chemical overlay.
Leslie: Wait, are you asking me out?
Leonard: I was going to characterize it as the modification of our colleague-slash-friendship paradigm with the addition of a date-like component, but we don't need to quibble over terminology.
Leslie: What sort of experiment?
Leonard: There's a generally accepted pattern in this area. I would pick you up. Take you to a restaurant. Then we would see a movie, probably a romantic comedy featuring the talents of Hugh Grant or Sandra Bullock.
Leslie: Interesting. And would you agree that the primary way we would evaluate either the success or failure of the date would be based on the biochemical reaction during the good night kiss?
Leonard: Heart rate, pheromones, et cetera. Yes.
Leslie: Why don't we just stipulate that the date goes well and move to the key variable?
Leonard: You mean kiss you now?
Leslie: Yes.
Leonard: Can you define the parameters of the kiss?
Leslie: Closed-mouth but romantic. Mint?

Howard: Sheldon, if you were a robot, and I knew and you didn't, would you want me to tell you?
Sheldon: That depends. When I learn that I'm a robot, will I be able to handle it?
Howard: Maybe, although the history of science fiction is not on your side.
Sheldon: Uh, let me ask you this: when I learn that I'm a robot, would I be bound by Asimov's Three Laws of Robotics?
Raj: You might be bound by them right now.
Howard: That's true. Have you ever harmed a human being, or, through inaction, allowed a human being to come to harm?
Sheldon: Of course not.
Raj: Have you ever harmed yourself or allowed yourself to be harmed except in cases where a human being would've been endangered?
Sheldon: Well, no.
Howard: I smell robot.

Sheldon: I've spent the past three-and-a-half years staring at greaseboards full of equations; before that, I spent four years working on my thesis; before that, I was in college, and before that, I was in the fifth grade.

Mrs. Cooper: [in trying to get Sheldon to go apologize to his boss Dr. Gablehauzer] Now listen here, Sheldon, I've been telling you since you were five years old, it's okay to be smarter than everyone else, but you can't go around pointing it out!
Sheldon: Why?
Mrs. Cooper: [sternly] Because other people don't like it!! Remember all the ass-kickings you used to get from the neighbor kids? Are you ready? Get your shoes, shirt and let's shove off!
Sheldon: [in a defeated tone of voice] There wouldn't have been any ass-kickings if that stupid death-ray would've worked.

Leonard: What did Penny mean, "you'd make a cute couple"?
Sheldon: Well, I assume she meant that the two of you together would constitute a couple that others might consider cute. An alternate, though somewhat less likely interpretation is that you could manufacture one. As in, "Oh, look, Leonard and Leslie made Mr. and Mrs. Goldfarb! Aren't they adorable?"
Leonard: If Penny didn't know that Leslie had already turned me down, then that would unambiguously mean that she, Penny, thought I should ask her, Leslie, out, indicating that she, Penny, had no interest in me asking her, Penny, out; but because she did know that I had asked Leslie out, and that she, Leslie, had turned me down, then she, Penny, could be offering me consolation - "That's too bad, you would have made a cute couple..." - while thinking, "good, Leonard remains available."
Sheldon: You're a lucky man, Leonard.
Leonard: How so?
Sheldon: You're talking to one of the three men in the Western Hemisphere capable of following that train of thought.
Leonard: Well, what do you think?
Sheldon: I said I could follow it, I didn't say I cared.

Penny: Leonard, I didn't know you played the cello.
Leonard: Yeah, my parents felt that naming me Leonard and putting me in advanced placement classes wasn't getting me beaten up enough.

[Kurt looking at Sheldon who is dressed as the Doppler Effect]
Kurt: So what are you, a zebra?
Sheldon: [to Leonard] Yet another child left behind.

Leonard: [To Kurt] A Homo habilis just discovering his opposable thumbs says what?
Kurt: [Confused] What?

Leonard: [seeing Sheldon trying to sit on the couch where Penny's head is] What are you doing?
Sheldon: Every Saturday since we've lived in this apartment, I have awakened at 6:15, poured myself a bowl of cereal, added a quarter-cup of 2% milk, sat on this end of this couch, turned on BBC America, and watched Doctor Who.
Leonard: Penny's still sleeping.
Sheldon: Every Saturday since we've lived in this apartment, I have awakened at 6:15, poured myself a bowl of cereal��
Leonard: You have a TV in your room. Why don't you just have breakfast in bed?
Sheldon: Because I am neither an invalid nor a woman celebrating Mother's Day.

Leonard: Sheldon, think this through. You're going to ask Howard to choose between sex and Halo.
Sheldon: No, I'm going to ask him to choose between sex and Halo 3. As far as I know sex has not been upgraded to include high-def graphics and enhanced weapons systems.
Leonard: You're right, all sex has is nudity, orgasms and human contact.
Sheldon: My point.

Sheldon: I'll have a Diet Coke.
Penny: OK, will you please order a cocktail? I need to practice mixing drinks.
Sheldon: Fine, I'll have a virgin Cuba Libre.
Penny: That's, um, Rum and Coke without the rum.
Sheldon: Yes.
Penny: So, Coke.
Sheldon: Yes. And would you make it Diet?
Penny: [sighs] There's a can in the fridge.
Sheldon: A Cuba Libre generally comes in a tall glass with a lime wedge.
Penny: Then swim to Cuba.
Sheldon: Bartenders are supposed to have people skills.