Leonard: Pretty cool about Howard, huh?
Sheldon: Dont talk to me as if nothing's happened between us. And yes, it sure is, buddy.
Leonard: For God's sake, will you stop with the Schrodinger stuff?
Sheldon: Would you prefer a simpler application of Heisenberg's uncertainty principle, in which I could either know where you are or whether I like you, but not both?
Leonard: You never stop talking, do you?

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: 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.

Professor Proton: Can I ask you a question?
Leonard: Yeah, sure.
Professor Proton: Why do you put up with Sheldon?
Leonard: Oh, you know because we're friends.
Professor Proton: Why?
Leonard: Wow, you ask really hard questions. Look, I know he can be aggravating, but what you have to remember is he's not doing it on purpose, it's just how he is. But he's also loyal and trustworthy and we have fun together.
Professor Proton: You know you're describing a dog?
Leonard: He did bite me once. But in his defense, I came up behind him while he was eating.
Professor Proton: They hate that.
Leonard: Sheldon is the smartest person I have met. He's a little broken and he needs me. And I guess I need him too.
Professor Proton: Why is that?
Leonard: Boy, you will not let this go, will you?

Penny: Wait, what is going on?
Sheldon: In case you have forgotten, Schrodinger's cat is a thought experiment.
Penny: No, no, no, no, I didn't forget. Um, there's this cat in a box and until you open it, it's either dead or alive or both. Although, back in Nebraska, our cat got stuck in my brother's camp trunk, and we did not need to open it to know there was all kinds of dead cat in there.
Amy: Homespun stories, knowledge of physics and a bosom that defies it. You're the whole package, aren't you?

Amy: It's not for us to judge. We're just here to provide comfort and support while you come to grips with what a despicable thing you've done.

Amy: Now Sheldon, I know you're a left handed monkey wrench but you seriously have a mortal enemy
Sheldon: Yes, in fact I have 61. Would you like to see the list?