Howard: So you're saying, if in the depths of despair she throws herself at you and demands you take her right there, right now, you'll just walk away?
Leonard: I said I'm her friend, not her gay friend.

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: 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.

Howard: You know, I'm really glad you decided to learn Mandarin.
Sheldon: Why?
Howard: Once you're fluent, you'll have a billion more people to annoy instead of me.

Leonard: Before you say anything, have you heard of Schrodinger's cat?
Penny: Actually, I've heard far too much about Schrodinger's cat.
Leonard: Good.
*Leonard and Penny kiss*
Penny: All right, the cat's alive. Let's go to dinner.

Raj: Incredible. You managed to screw up the screw up.