Sheldon: Mailman's here!
Leonard: Aw, remember when he used to get that excited to see us?

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.

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: My point is, while you're spending all this time on your own, building computers or practicing your cello, what you're really doing is becoming interesting. When people finally do notice you, they're gonna find someone a lot cooler than they thought. And for those of you that were popular in high school, it's over, sorry. Thank you. Congratulations.

Sheldon: Well, of course I'm worried about you, I want you to be safe.
Amy: And I want you to be safe.
Sheldon: I will be. I'll have my friends with me. If anything should go wrong, I can use them as human shields.

Sheldon: *knock knock knock* Dr. Wolcott? *knock knock knock* Dr. Wolcott? *knock knock knock* Dr. Wolcott? [sound of many locks clacking]
Howard: That's a lot of locks.
Leonard: Mm. That was a lot of knocks, they were made for each other.

Sheldon: Do you really know how to Riverdance?
Amy: You tell me.
Sheldon: I'm the only man you do that for.