Sheldon: I've been studying how to make people laugh. They say comedy is tragedy plus time. *Looks at his watch and gets up* Let's tickle some ribs!

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.

Amy: Do you have any idea how hard it is to laugh at a knock knock joke that starts "Knock Knock Knock, Amy. Knock Knock Knock, Amy. Knock Knock Knock, Amy"?

Bernadette: (Shouting from the bathroom) How many times do I have to tell you to replace the toilet paper when it's empty?
Howard: I'm in the middle of something.
Bernadette: So am I!

Penny: I just got a part on a TV show.
Amy: Congratulations!
Leonard: That's great. Guys ...
The guys: Yeah ...
Amy: What's the show?
Penny: NC - I I? or, you know, NC - S T D. I don't know. It's the one with all the letters.