Sheldon: There's an economic concept known as a positional good in which an object is only valued by the possessor because it's not possessed by others. The term was coined in 1976 by economist Fred Hirsch to replace the more colloquial, but less precise "neener-neener".

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 would you guys do if you were me?
Wolowitz: I would take Sheldon to Switzerland.
Leonard: Seriously?
Wolowitz: Absolutely. And I'd leave him there.

Sheldon: It was you. I touched you!
Penny: Happy Valentine's Day.

Penny: I think I caught the flu. *Throwing up*. Or the plague!