(Sheldon notices Penny taking Leonard to his bedroom)
Sheldon: What's going on?
Penny: Get your noise-cancelling headphones, 'cause it's gonna get loud.
Sheldon: Oh, not this again.

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: That's not afternoon. That's prevening.
Howard: What?
Sheldon: It's a time of day I invented. It better defines the ambiguous period between afternoon and evening. Prevening. I'm fairly certain it will catch on as it fills a desperate need.
Raj: Right, okay. What are you doing tomorrow prevening?
Sheldon: Well, tomorrow's Saturday. Saturday night is laundry night, so I'll be spending the prevening pre-sorting and pre-soaking.

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

Sheldon: As a native Texan, I must say I've never heard the phrase "yeeehaw" used in quite that context.

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?

Leonard: Relax, it's just a dirty sock.
Sheldon: How on earth can you say "dirty sock" and "relax" in the same sentence?

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

Sheldon: This is the temperature you agreed to in the roommate agreement.
Leonard: Aw, screw the roommate agreement!
Sheldon: No, you don't screw the roommate agreement. The roommate agreement screws you.

Leonard: You know what, go to Hell and set their thermostat.
Sheldon: I don't have to go to Hell. At 73 degrees, I'm there already!

Sheldon: Oh, Ubuntu. You're my favorite Linux-based operating system.

TV Announcer: Up next Babylon 5.
(Sheldon looks at Leonard)
(Penny listening to Sheldon and Leonard argue from her apartment)
Leonard: You're not even watching it.
Sheldon: I can hear it.
Leonard: The dialogue offends you?

Sheldon: When do you evacuate your bowels?
Leonard: When I have to.
Sheldon: When you have to? I'm sorry I don't rent to hippies.

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: 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.