Leonard: Guys, everyone is involved in this, okay? Howard's invention, Sheldon's math, my original theory that space-time was like a supercooled liquid. Which I'm sure Penny would've mentioned if she wasn't working on that hangnail right now.
Penny: What?

Leonard: What would you be if you were attached to another object by an inclined plane, wrapped helically around an axis?
Sheldon: Screwed?
Leonard: There you go.

Leonard: Penny, as a scientist, my job is to figure out why things happen. But I don't think I'll ever understand how someone like me could get to be with someone like you. You know maybe I don't need to understand it, I just need to be grateful. I love you, Penny.

Sheldon: This song is never going to stop. Have you ever dealt with something so relentlessly irritating?
Leonard: That's a trick question, right?

Leonard: Hang on. Maybe there should be a "no insult" clause about me, too.
Sheldon: Do you still like cilantro?
Leonard: Yeah.
Sheldon: You're tying my hands here.

Howard: See, he's not wearing a tie.
Leonard: Well, he's a patent attorney. Maybe his tie is pending.

Leonard: Hold on, hold on. So the three of us do all the work and only end up with 25%? Patent Attorney: Dr. Hofstadter, this university has been paying your salaries for over ten years. Did you think we do that out of the goodness of our hearts?
Leonard: Well, until you just said that mean thing, kinda.