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.

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?

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

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

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

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.

Howard: So I'm almost done writing the song for Bernadette. Are you cool playing the cello?
Leonard: If by cool you mean willing to, yes. If by cool you mean cool, clearly you've never seen me play the cello.