Dealer: Huh. All these years, I've been using stalemate, when I really mean impasse. I feel foolish.
Leonard: I don't think it matters if this is a stalemate or an impasse or a Mexican standoff. What are we gonna do here?
Dealer: Oh, whoa, whoa, how can it be a Mexican standoff? Everybody knows you need three sides for that.
Sheldon: Not necessarily. Uh, many argue the essence of a Mexican standoff is that no one can walk away from the conflict without incurring harm.
Dealer: Hmm, I don't follow.
Sheldon: Let me give you an example. Earlier today, I decoded the headers on your e-mail, and I know that your name is Kenneth Fitzgerald.
From that, I figured out where you live and where you work.
Now, to make this a Mexican standoff, I would say something like, uh, "You give us the helium or I'll turn you in to the authorities."
Dealer: Is that a threat?
Sheldon: Yeah, exactly. See, you're getting it.
Dealer: Yeah, well, I know where you work, all right? And if you mess with me, I'll report you, then I'll pound your asses into the ground.
Sheldon: Perfect! Now we really are in a Mexican stand-off.

Raj: I don't like bugs, okay. They freak me out.
Sheldon: Interesting. You're afraid of insects and women. Ladybugs must render you catatonic.

Sheldon: Scissors cuts paper, paper covers rock, rock crushes lizard, lizard poisons Spock, Spock smashes scissors, scissors decapitates lizard, lizard eats paper, paper disproves Spock, Spock vaporizes rock, and as it always has, rock crushes scissors.

Sheldon: Why are you crying?
Penny: Because I'm stupid.
Sheldon: That's no reason to cry. One cries because one is sad. For example, I cry because others are stupid, and that makes me sad.

Leonard: What are we going to do?
Sheldon: Perform the experiment immediately.
Leonard: I'd love to, but we need liquid helium and our shipment's on back order for a month.
Sheldon: A month? What? Are you kidding me? That would have been a good time for you to soften the blow.
Leonard: That shirt brings out the blue in your eyes.
Sheldon: Thank you. Aren't you sweet?

Sheldon: He has glasses and I'm a know-it-all. We are not built for prison.

Sheldon: Uh, but this is violating university code.
Leonard: A little, but if I may quote Einstein, "The pursuit of science calls us to ignore the rules set by man"
Sheldon: Huh. All right, do it. Tell him we're in.
Leonard: Done.
Sheldon: I can't find that quote on the Internet. Did you make that up?
Leonard: Before I answer, may I just say your skin has never looked better.
Sheldon: Aren't you just made of sugar.