Raj: You can't let this stop you. Almost any scientific advancement can be used for destructive purposes.
Amy: It's true. Even Einstein's theory of relativity was later applied to the development of nuclear weapons.
Penny: E equals MC squared. Yeah. E is for energy, M for mass, and C for the speed of light.
Amy: How do you know that?
Penny: Oh, Leonard mumbles it when he wants sex to last longer.

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

Raj: [to Amy] If you were having Sheldon's baby, would you really want him in the room?
Penny: Yeah, if he's in the room when they're making the baby, I'll give you $10.

Penny: I mean, who even reads Scientific American?
Leonard: It's kind of a big deal.
Penny: If it's such a big deal, how come the biggest celebrity they could get for the cover is a molecule?

Leonard: Hey, did you ever think about the military applications for the guidance system?
Sheldon: Of course.
Leonard: Does it bother you?
Sheldon: No, it did at first. But then I talked it through with Frank and Alicia, and they really helped put things into perspective.
Leonard: Who are these people?
Sheldon: Leonard, friends are like toilet paper. It's good to have extras under the sink.

Raj: Yeah, okay, just do me a favor and stop talking about how great Claire is.
Zack: Anything for you, my little foreign friend.

Raj: Hey, dude, you're killing me with Claire.
Zack: What are you talking about?
Raj: I mean, come on, look at you. You're classically handsome, you've got a swimmer's body. Next to you, I look like me.