Dr. Cox: What is it with friends and the whole wanting to be in your life thing?
J.D.: It's selfish is what it is.

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.

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?

Excuse me, explain to me an organizational system where a tray of flatware on a couch is valid? Now, I'm just inferring that this is a couch, because the evidence suggests that the coffee table is having a tiny garage sale.

Sheldon: I can't believe he fired me.
Leonard: Well, you did call him a "glorified high school science teacher whose last successful experiment was lighting his own farts."
Sheldon: In my defense, I prefaced that with, "with all due respect."

Sheldon: This car weighs, let's say, 4,000 pounds. Now add 140 for me, 120 for you...
Penny: 120?!
Sheldon: Oh, I'm sorry. Did I insult you? Is your body mass somehow tied into your self-worth?

I don't know how, but she is cheating! Nobody can be that attractive and this skilled at a video game.

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

Leonard: Sheldon, are you worried about your safety?
Sheldon: No, I imagine if you were going to kill me, you'd have done it a long time ago.
Leonard: That's very true.

Every family in America has a relative holed up in a garage somewhere huffing paint thinner.

Sheldon: Here's the problem with teleportation.
Leonard: Lay it on me.
Sheldon: Assuming a device could be invented, which would identify the quantum state of matter of an individual in one location and transmit that pattern to a distant location for reassembly. You would not have actually transported the individual, you would have destroyed him in one location and recreated him in another.
Leonard: How about that.
Sheldon: Personally, I would never use a transporter because the original Sheldon would have to be disintegrated in order to create a new Sheldon.
Leonard: Would the new Sheldon be in any way an improvement on the old Sheldon?
Sheldon: No, he would be exactly the same.
Leonard: That is a problem.

Engineering, where the semi-skilled laborers execute the vision of those who think and dream.

Sheldon: So, you're saying that friendship contains within it an inherent obligation to maintain confidences?
Penny: Well, yeah.
Sheldon: Interesting. One more question—and perhaps I should have led with this—when did we become friends?

Leonard: What do you mean, you're moving out? Why?
Sheldon: There doesn't have to be a reason.
Leonard: Yeah, there kinda does.
Sheldon: Not necessarily. This is a classic example of Münchhausen's Trilemma. Either the reason is predicated on a series of sub-reasons leading to an infinite regression, or it tracks back to arbitrary axiomatic statements, or it's ultimately circular, i.e. I'm moving out because I'm moving out.
Leonard: I'm still confused.
Sheldon: Leonard, I don't see how I could have made it any simpler.

Leonard: How could you just sit there and let them spy on me?
Sheldon: They were clever, Leonard. They exploited my complete lack of interest in what you were doing.

Everybody has a date. Even you Mario, going after Princess Peach. What am I doing? I'm just enabling you.

Penny: I am going to introduce your friend to a world of hurt.
Leonard: You don't want to get into it with Sheldon. The guy is one lab accident away from being a super villain.

I am not going to watch the Clone Wars TV series until I've seen the Clone Wars movie. I prefer to let George Lucas disappoint me in the order he intended.

It's very simple. Scissors cuts paper, paper covers rock, rock crushes lizard, lizard poisons Spock, Spock smashes scissors, scissors decapitates lizard, lizard eats paper, paper disproves Spock, Spock vaporizes rock, and—as it always has—rock crushes scissors

You know, I've given the matter some thought, and I think I'd be willing to be a house pet to a race of super-intelligent aliens.