Leonard: Damnit.
Priya: Wow, Leonard, already?
Leonard: No no no. The screen froze.

Howard: You gotta like this. The girlfriend, the ex-girlfriend bonding over your rooty-tooty stinky booty.
Leonard: Kill me.
Sheldon: It wouldn't help. The human body is capable of being flatulent for hours after death.

Leonard: If my PE teachers told me this is what I was training for I would have tried a lot harder.
Penny: Do or do not, there is no try.
Leonard: Did you just quote Star Wars?
Penny: I believe I quoted Empire Strikes Back.
Leonard: Oh my God. I'm lying in bed with a beautiful woman who can quote Yoda.

Sheldon: Are you upset about something?
Leonard: What was your first clue?
Sheldon: Well, it was a number of things: first, the late hour; then your demeanor seems very low energy; plus your irritability...
Leonard: Yes, I'm upset!
Sheldon: Huh, I don't usually pick up on those things. Good for me.
Leonard: Yeah, good for you.
Sheldon: Oh, wait, did you want to talk about it?
Leonard: I don't know, maybe.
Sheldon: Wow, I'm on fire tonight

Leonard: Oh, geez, I - I don't know if I can ditch Priya two nights in a row.
Raj: Oh, come on, man. Bros before... my sister.

Sheldon: Looking out at your fresh young faces, I remember when I, too, was deciding my academic future as a lowly graduate student. Of course, I was fourteen. And I had already achieved more than most of you could ever hope to, despite my 9:00 bedtime. Now, there may be one or two of you in this room who has what it takes to succeed in theoretical physics, although it's more likely that you'll spend your scientific careers teaching fifth graders how to make papier-mâché volcanoes with baking soda lava.
Leonard: Oh, good God.
Sheldon: In short, anyone who told you that you would someday be able to make some significant contribution to physics, played a cruel trick on you—a cruel trick indeed. Any questions? ... Of course not. I weep for the future of science

I haven't seen him this stuck since he tried to figure out the third Matrix movie.

Leonard: Beekeeper to King 12. I capture your pope and release the swarm. Checkmate on Sheldon.
Sheldon: I knew I should've given my pope the jet pack.

Leonard: What do you mean, you're moving out? Why?
Sheldon: There doesn't have to be a reason.
Leonard: Yeah, there kinda does.
Sheldon: Not necessarily. This is a classic example of Münchhausen's Trilemma. Either the reason is predicated on a series of sub-reasons leading to an infinite regression, or it tracks back to arbitrary axiomatic statements, or it's ultimately circular, i.e. I'm moving out because I'm moving out.
Leonard: I'm still confused.
Sheldon: Leonard, I don't see how I could have made it any simpler

Leonard: How could you just sit there and let them spy on me?
Sheldon: They were clever, Leonard. They exploited my complete lack of interest in what you were doing

Leonard: No, just you and me.
Penny: Have you thought this through?
Leonard: Yes, and I think we should go anyway.

Leonard: You know what baffles me Sheldon?
Sheldon: Based on your academic record, I could guess any number of things

TBBT Quotes

Oh, Bernadette, please play my clarinet.

Raj's poem

Sheldon: I'll have a diet Coke.
Penny: Can you please order a cocktail? I need to practice mixing drinks.
Sheldon: Fine... I'll have a virgin Cuba Libre.
Penny: That's... rum and Coke without the rum.
Sheldon: Yes, and would you make it diet?