Penny: I mean, come on, when was the last time you did something totally selfish without worrying about what anyone else wanted?
Leonard: Uh, according to my mother, I took my sweet time being born.
Penny: How is that selfish?
Leonard: Apparently, she had dinner reservations.

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.

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: 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.

Amy: Wow. Déjà vu.
Sheldon: Amy, you're a neuroscientist. you know the latest research into déjà vu suggests it's nothing but the frontal regions of the brain attempting to correct an inaccurate memory.
Amy: You telling me stuff I already know is definitely déjà vu.

Sheldon: How can I tell if I'm doing something for a noble reason or a selfish reason?
Amy: Try saying the thing in your head and see if you can add the words, "That'll show 'em."

Sheldon: Leonard's about to demand a job that I don't think the university will give him. I'm worried he's making a giant mistake. But maybe I only think that because deep down I don't want him to succeed.
Amy: The fact that you're worried about your motivation supports the idea that you genuinely care for your friend.
Sheldon: I do. Thank you, Amy. You know what? After I've talked to Leonard, you've earned yourself a bonus lecture on Sponge Hulk.
Amy: That'll show me.