Amy: Penny said she's not sure she wants to be Leonard's girlfriend anymore.
Sheldon: Wrong. She just took a sip from his Diet Dr. Pepper.
Amy: So?
Sheldon: So, if she wants to end her pair-bond with Leonard, why on earth would she guzzle a witches' brew of his soda and spit?

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.

Sheldon: If you're going to replace Wolowitz, I need to know a little bit more about you.
Stuart: All right.
Sheldon: Wolowitz went to MIT. What's your educational background?
Stuart: I went to art school.
Sheldon: Equally ridiculous. Let's go.

Sheldon: Settle down there, fake Wolowitz. No one likes a kiss-up.

Sheldon: Penny, please don't hurt my friend.