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" but while thinking "good, Leonard remains available."
Sheldon: You're a lucky man Leonard.
Leonard: How so?
Sheldon: You're talking to one of 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.

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?

Sheldon: Given the reaction to my costume, this party is a scathing indictment of the American educational system.
Kurt: You're a zebra, right?
Sheldon: (to Leonard) Yet another child left behind.

Howard: Wait till you see this.
Raj: It's fantastic. Unbelievable!
Leonard: See what?
Howard: (Putting in DVD) It's a Stephen Hawking lecture from MIT in 1974.
Leonard: This isn't a good time.
Howard: (Imitating Stephen Hawking) It's before he became a creepy computer voice.

Leonard: Our babies will be smart and beautiful.
Sheldon: Not to mention imaginary.

Sheldon: Sorry, I'm late.
Leonard: What happened?
Sheldon: Nothing. I just didn't want to come.

Leonard: Is this the high-IQ sperm bank?
Althea: If you have to ask, maybe you shouldn't be here.

Penny: Hey, guys! My friends and I got tired of dancing so we came over to have sex with you.
(The guys continue to play Halo).
Penny: Told ya.
(Penny and her friends leave).
Sheldon: Why did you hit pause?
Leonard: I thought I heard something.
Rajesh: What?
Leonard: No, never mind.

Penny: (Upset, about Kurt) 4 years, I lived with him. 4 years! That's like as long as high school.
Sheldon: It took you 4 years to get through high school?

Wolowitz: Love is not a sprint, it's a marathon, a relentless pursuit that only ends when she falls into your arms - or hits you with the pepper spray.

Leonard: Is this the stuff you want me to try on?
Penny: No this is the stuff I want you to throw out. Seriously, don't even give it to charity. You won't be helping anyone.

Howard: By the way, where did you get that loofah mitt? Yours reaches places that mine just won't.
Penny: You used my loofah?
Howard: More precisely, we used your loofah. I exfoliated her brains out!

Sheldon: Oh, what fresh hell is this?

Raj: Incredible. You managed to screw up the screw up.

Sheldon: (In Mandarin) Show me your mucus. Your mucus!
Chen: (Mandarin) Blow your own nose and go away!
Sheldon: (Mandarin) This is not a tangerine bicycle. Show me your mucus!
Chen: Crazy man. Call the police.
Sheldon: (Mandarin) No, don't call the library. Show me your mucus.