Sheldon: A fear of heights is illogical. A fear of falling, on the other hand, is prudent and evolutionary.

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.

Wolowitz: *After he fixed Sheldon's algorithm* Gee, why can't Sheldon get a friend?

Sheldon: What part of an inverse tangent approaching an asymptote don't you understand?

Sheldon: "Barney Bunny has two daddies now." Probably something about homosexual rabbits.