Sheldon: I've changed. Like the frog who's put in a pot of water that's heated so gradually, he doesn't realize he's boiling to death.
Penny: Or you're the frog who's been kissed by the princess and turned into a prince.
Leonard: Or you're just a tall, annoying frog.

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.

Bernadette: I think what we're all trying to say is that you don't seem to be remembering how traumatic the experience was for you.
Raj: Like how women often forget the pain of childbirth.
Mike Rostenkowski: Like a woman. Great analogy.

Amy: I'm not surprised you want to end the relationship. I'm a little surprised you didn't get AppleCare.

Amy: You don't need to explain yourself to him.
Sheldon: (To Leonard) I don't need to explain myself to you!
Amy: You're sick of his nonsense and you're ready to move in with me.
Sheldon: (To Leonard) Keep the table. We don't use that space.
Amy: Damn it. I got cocky.