Leonard: And this is a high-pulse laser with a BBO crystal. It's pretty cool. It emits photons in discrete bursts.
Beverly Hofstadter: Huh. Very impressive.
Leonard: But?
Beverly Hofstadter: But what, dear?
Leonard: Oh, I don't know. It's just, usually there's a "but" followed by something that makes me feel bad.

Leonard: I'm done enabling him. Like, this is his spot and-and the thermostat has to be set to his comfort level, even though he doesn't even live here anymore and I'm always chilly.
Raj: Is that why you wear a hoodie all the time?
Leonard: Why would-- Yes! To accommodate Sheldon! And what-what about this-this thing? Why is it here? I'll tell you why. Because it was here when I moved in, and, for no earthly reason, he forbade me to touch it.
Amy: Well, if you don't like it, get rid of it. Put it in the closet.
Leonard: You know what, I will. [Leonard tries to move the helix structure. Lots of little beads fall off and come crashing to the floor]
Raj: I bet that's the reason.

Sheldon: Well done. You know, you're proving to be an invaluable part of my entourage.
Leonard: Cool.

Penny: Leonard, I can't go home. I have to be there for Amy.
Leonard: Yeah. I was thinking that, too. As angry as I am at Sheldon, I still want to see him win that medal.
Penny: It's so strange. No matter how thoughtless and selfish he is, I still love him.
Leonard: If you think about it, he has kind of been our practice kid.
Penny: Like when you make pancakes and the first one comes out a little wonky?
Leonard: The university prefers "quirky."

Doug: What's up, bro?
Leonard: Uh, nothing much... Bro!

Leonard: I'm so proud of you.
Penny: They haven't even got to my scene yet.
Leonard: I know, but you're going to be a TV star and you haven't left me yet. That takes guts!

Leonard: (on the phone) Yes, how much for 100 long-stem red roses? Really? How much for three?

Leonard: Oh, okay. Good, good. So it's cool if I cry a little?
Penny: Yeah, I probably wouldn't.
Leonard: Yeah ... *wipes tears from his right eye*.

Leonard: Do you really want him to write back?
Sheldon: I do. And no matter how he responds, I'm going to destroy him with a picture of a bored cat saying "Oh, really?"
Leonard: Mee-wow.

Leonard: Okay, look. Instead of fighting, why don't we dim the lights, get naked and make a baby?

Was trying to lighten the mood. It's not easy. You try it.

Leonard: Sheldon, we both agreed to do this.
Sheldon: It's a waste of time. I might as well explain thermodynamics to a bunch of Labradoodles.
Leonard: If you don't do this, I won't take you to the comic book store.

Leonard: Maybe it's a shipping problem.
Howard: What?
Leonard: Maybe Wesley Snipes and Toucan Sam just got action figures that look like you guys.

Leonard: The funeral's on Sunday.
Sheldon: But that's Star Wars day.
Leonard: Yeah. Off all the things about this that are sad, that might not be number one.

Sheldon: It's like when I thought there was possum in my closet. Did I sit around wondering? No, I sent Leonard in with a pointy stick and a bag.
Leonard: I killed his chewbacca slippers.

Leonard: "Upon review, I've changed my mind about the Cooper-Hofstadter hypothesis that space-time is like a super-fluid. In fact, it's inspired me to come up with my own theory. Maybe space-time is like two clowns with their heads in a bucket. Much like Cooper and Hofstadter."