Leonard: She didn't dump me. We were just in different places in the relationship.
Sheldon: I fail to see how a relationship can have the qualities of a geographical location.
Wolowitz: It's very simple. Leonard was living in a little town called "Please don't leave me", while Penny had just moved to the island of "Bye-bye!"

Zack: Hey, I want to see this laser thing.
Penny: Oh, but what about the party?
Zack: It's a surprise party, doesn't matter when we get there.

Sheldon: Hello, Amy Farrah Fowler. I'm sorry to inform you that you've been taken in by unsupportable mathematics designed to prey upon the gullible and the lonely. Additionally, I am being blackmailed with a hidden dirty sock.
Amy: If that was slang, I'm unfamiliar with it. If it was literal, I share your aversion to soiled hosiery.

Sheldon: I should've brought an umbrella.
Leonard: What for? It's not going to rain.
Sheldon: I know that, but with skin as fair as mine, moon burn is a real possibility.
Howard: That's a bazinga, right?
Sheldon: One of my best, don't you think?

Zack: Cool, it's gonna be in 3-D!

Sheldon: Incidentally, one can get beaten up in school simply by referring to oneself as one.

Howard: *Noticing Raj peeking through someone's window using the telescope* Oh, Raj, no. Billions of dollars have gone into inventing the Internet and filling it with pictures of naked women, so we don't have to peep through windows.

Raj: The Good Wife is on. I tell you, this is my new Grey's Anatomy.

Sheldon: Roommates agree that Friday nights shall be reserved for watching Joss Whedon's brilliant new series Firefly.
Leonard: Does that really need to be in the agreement?
Sheldon: We might as well settle it now, it's going to be on for years.

Leonard: Dr. Cooper?
Louis: No, you want the crazy guy next door.

Penny: Okay, Babydoll Pink, let's see if you can cover up the fact that I got my dad's feet.

Sheldon: What's the sixth noble gas?
Leonard: Uh, radon?
Sheldon: Are you asking me or telling me?
Leonard: Telling you?
(Sheldon gives Leonard a stern look)
Leonard: Telling you.

Sheldon: Last question. In a post-apocalyptic world, which task would you assign the highest priority? Locating a sustainable food source, re-establishing a functioning government, procreating, or preserving the knowledge of mankind.
Leonard: Uh, I'm gonna go with preserving the knowledge.
Sheldon: That's correct. FYI, I would have accepted any answer other than procreating.

Sheldon: I assure you, you'll be sorry that you wasted your money on an iPod when Microsoft comes out with theirs.
Rajesh: Do you have an opinion about everything?
Sheldon: Yes.
Howard: And you just assume you're right?
Sheldon: It's not an assumption.

Leonard: Not only that Sheldon saved my life, but that he didn't report me to the landlord, or the police, or homeland security.