Penny: So, what's new in the world of physics?
Leonard: Nothing.
Penny: Really, nothing?
Leonard: Well, with the exception of string theory, not much has happened since the 1930s. And you can't prove string theory, at best you can say “Hey, look, my idea has an internal logical consistency.”
Penny: Ah. Well I'm sure things will pick up.

Leonard: What am I supposed to do?
Penny: Err, keep your mouth off other women.

Penny: At one point, they had me figure out how to get a banana out of a puzzle box.
Leonard: Wait, Sheldon gave me a banana in a box. He was testing me, too.
Penny: Unbelievable.
Leonard: And how could a chimp even solve that? That was impossible.
Penny: Really? You couldn't get it out?

Sheldon: Woman, you are playing with forces beyond your ken.
Penny: Yeah, well your Ken can kiss my Barbie.

Sheldon: I think that you have as much of a chance of having a sexual relationship with Penny as the Hubble telescope does of discovering at the center of every black hole is a little man with a flashlight searching for a circuit breaker.

Howard: Sheldon, if you were a robot and I knew and you didn't, would you want me to tell you?
Sheldon: That depends. When I learn that I'm a robot, will I be able to handle it?
Howard: Maybe, although the history of science fiction is not on your side.

Wolowitz: Love is not a sprint, it's a marathon, a relentless pursuit that only ends when she falls into your arms - or hits you with the pepper spray.