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: Are you still mad about the sperm bank?
Leonard: No!
Sheldon: Do you want to hear an interesting thing about stairs?
Leonard: Not really.
Sheldon: If the height of a single step is off by as little as two millimeters most people will trip.
Leonard: I don't care—two millimeters?! That doesn't seem right.
Sheldon: No, it's true! I did a series of experiments when I was twelve; my father broke his clavicle.

Penny, there's only one cookie with something in the middle that solves life's problems, and that's an Oreo. Or a Nutter Butter, if you're in a pinch.

Sheldon