Sheldon: As a native Texan, I must say that I've never heard the phrase "yee haw" used in quite that context.
Penny: Oh God.
Sheldon: "Oh God." That I've heard on multiple occasions.

Sheldon: I should have brought an umbrella.
Leonard: What for? It's not gonna rain.
Sheldon: I know that, but with skin as fair as mine, moon burn is a real possibility.

Sheldon: Are you asking me or telling me?
Leonard: Telling you?

Sheldon: That's not an apology; that's simply an acknowledgment that I was right.
Leonard: Okay, I'm sorry.
Sheldon: There you go.

I assure you, you'll be sorry you wasted your money on an iPod when Microsoft comes out with theirs.

Leonard: What am I doing in your spam folder?
Sheldon: I put you there after you forwarded me a picture of a cat playing the piano entitled, "this is funny."

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: Might as well settle it now; it's going to be on for years.

Wheaton: Embrace the Dark Side!
Sheldon: That's not even from your franchise!

Can I get you something? A feminine hygiene product or a bowel-regulating yogurt?

Dr. Plimpton, Penny is a waitress who doesn't understand the role gasoline plays in the internal combustion engine.

Leonard: Well, it wasn't my fault.
Sheldon: The implication being that you somehow tripped and fell into her lady parts?

Dr. Plimpton: What if there's a disaster that destroys all of the USB ports?
Sheldon: Then there's really no reason to live, is there?

TBBT Quotes

Sheldon: Why do you have the Chinese character for "soup" tattooed on your right buttock?
Penny: It's not "soup," it's "courage."
Sheldon: No it isn't. But I suppose it does take courage to demonstrate that kind of commitment to soup.
Penny: How'd you see it? You said you wouldn't look.
Sheldon: Sorry. As I told you, the hero always peeks.

Penny: Hey, Sheldon, did you change your Wi-Fi password again?
Sheldon: Yes, it's "Penny, get your own Wi-Fi." No spaces.