Leonard: Ethyl alcohol inhibits electrical conduction in the nerve cells and stimulates re-uptake receptors of inhibitory neurotransmitters like gamma-amino butyric acid.

Leonard: I bet I could throw a rock in this room and come up with three better friends!

Penny: What did you tell them?
Leonard: Nothing bad, just that last night was fine.
Penny: Fine? You said it was fine?
Leonard: Yeah, it's a perfectly good word. You put it in front of wine or dining, and you've really got something.

Leonard: When he wasn't happy, we wanted to kill him. There was even a plan. We were going to throw his Kindle outside, and when he went to get it, lock the door and let him freeze to death.
Sheldon: That seems like a bit of an overreaction.
Leonard: No, the overreaction was the plan to tie your limbs to four different sled-dog team and yell "Mush!"

Leonard: Hey. Listen, since we got, you know, interrupted last night, I didn't have a chance to give you this.
Penny: Oh, Leonard, you shouldn't have. Oh, boy! What is it?
Leonard: It's a snowflake. From the North Pole.
Penny: Are you serious?
Leonard: Uh-huh. It'll last forever. I preserved it in a one percent solution of polyvinyl acetal resin.
Penny: Oh, my God. That's the most romantic thing anyone's ever said to me that I didn't understand.
Leonard: It's actually a pretty simple process. You see, cyanoacrylate are monomers which polymerize on... [Penny kisses him]

Sheldon: Everyone at the university knows I eat breakfast at 8:00 and move my bowels at 8:20.
Leonard: Yes, how did we live before Twitter?

Sheldon: I'm a theoretical physicist, a career I chose in no small part because it's indoors. But if I'm able to detect slow-moving magnetic monopoles there, I will be the first scientist to confirm string theory. People will write books about me. Third-graders will create macaroni-art dioramas depicting scenes from my life.
Leonard: Sure, maybe a tableau of me trying to pummel you to death.

Leonard: What about the really long hug? What did that mean?
Penny: That wasn't a long hug.
Leonard: It was at least five Mississippis. A standard hug is two Mississippis tops.

Leonard: Thanks for closed captioning my pain, Raj.

Leonard: Just think. Thanks to your hard work, an international crew of astronauts will boldly go where no man has gone before.

Penny: Well, does it bother you, me going out with one of your friends? 'cause you know, you and me.
Leonard: No, no that's the past. I'm really more of a right now kind of guy. You know, living in the moment. Although I do have to live a little in the future, 'case, well, that's my job. Of course, my fondness for classic science fiction does draw my attention backwards, but those stories often take place in the future. In conclusion, no, it doesn't bother me.

Penny: Well, In that case, do you mind giving me some advice?
Leonard: About Stuart? Love to.
Penny: He's very shy, how do I make him feel more comfortable around me?
Leonard: Well, uh, first of all, don't underestimate the value of discomfort.
Penny: Really?
Leonard: Well, yeah, Stuart thrives under pressure, that's why he works in a comic book store.

Leonard: Hey Stuart.
Stuart: You busy?
Leonard: Um…
Howard: Classified, Leonard.
Leonard: Yeah, it's a regular Manhattan Project.

Penny: Morning. What’s up?
Leonard: Nothing. We just pulled an all-nighter trying to fix a zero-gravity ... pasta maker.

Leonard: Hey, Stuart, I need to talk to you.
Stuart: Sure, what's up?
Leonard: I think I gave you bad advice about Penny, and I want to apologize.
Stuart: No, your advice was great.
Leonard: It was?
Stuart: Yeah, going slow really worked.
Leonard: You're kidding. Never worked for me.