Penny: What's thoughtful is everything you do. Here, look at this. This is the plane ticket you bought me when I was too poor to go home for the holidays. And the rose you left on my windshield just because. Here's the thank you letter you wrote me after the first time I slept with you. All eleven pages of it.
Leonard: I can't believe you saved all this stuff.
Penny: Of course I did, it's you.
Leonard: Come here. ... Is that a pregnancy test?
Penny: Oh yeah, just the first one. I didn't save them all.

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

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

Leonard: If I take it off, Sheldon wins.
Penny: Sweetie, every night you don't kill him in his sleep, he wins.

Sheldon: Sheldon Cooper does not get lucky.
Amy: You and me both, brother.

Sheldon: I've got to find a way to stop this thing.
Leonard: Buddy, I don't think you can. Once it's out there, it's out there. This thing is like the science equivalent of a sex tape.
Sheldon: Frankly, I'd prefer a sex tape.
Leonard: You don't know what a sex tape is, do you?
Sheldon: No.

Bernadette: Great news. A raccoon virus just crossed the species barrier and can now infect humans.
Raj: Why is that great news?
Bernadette: In the pharmaceutical business we have a saying: mo' infections, mo' money.