Leonard: Howard, this is big science. You could be the engineer who builds the equipment that puts us on the cover of magazines.
Howard: I could also be the engineer who builds the crossbow that kills Sheldon.

Howard: Hey, you want to make sure he gets nowhere with Penny without jeopardizing your friendship with either of them?
Leonard: I'm listening.
Howard: Just tell him to do everything you've done with her for the last two years.

Sheldon: *knock knock knock* Leonard? (x3)
Leonard: What, Sheldon!? What, Sheldon!? What, Sheldon!?
Sheldon: Tell me what you see here.
Leonard: The blunt instrument that will be the focus of my murder trial?

Sheldon: I wouldn't tell you the secret. Sssh!
Leonard: What secret? Tell me the secret.
Sheldon: Mom smokes in the car. Jesus is okay with it, but we can't tell dad.
Leonard: Not that secret, the other secret.
Sheldon: I'm Batman! Ssssh!

(Sheldon smiles in a grotesque way).
Howard: Oh crap that's terrifying.

Penny: Here you go, (to Leonard) Quesadilla, (to Howard) Salad, (to Raj) Here's your pizza. And thanks to Sheldon's heated discussion with my manager, one barbecue bacon cheeseburger, barbecue sauce, bacon, and cheese on the side.
Sheldon: Thank you!
Penny: Go ahead. Eat it. I dare you!

Leonard: Penny, you don't want to get into it with Sheldon. The guy's one lab accident away from being a super villain.

Wolowitz (watching America's Next Top Model): Oh, look! That's the future Mrs. Wolowitz. No, wait! That's the future Mrs. Wolowitz. With her head in the lap of... what a coincidence... it's the future Mrs. Wolowitz.
Leonard: Yeah, and they can all move in with you and your mother. The current Mrs. Wolowitz.

Leonard: What were you doing at Penny's?
Sheldon: Well, we had dinner, played some games, and then I spent the night. Oh, and you'll be happy to know that I now have a much better understanding of 'friends with benefits.'

Mrs. Wolowitz Should I ask Leonard to bring over your homework?
Howard: I don't have homework. I'm a grown man with a master's degree in engineering.
Mrs. Wolowitz Excuse me, Mr. Fancy Pants. Want me to get you a popsicle?

Raj: What do you say, Howard?
Howard: I say Vegas baby!
Raj: What are you gonna tell your mother?
Howard: Sea World baby!

Hooker: What's your name?
Raj: Rajesh Ramayan Koothrappali.
Hooker: Hello Rajesh Ram...Hello Rajesh.

Penny: Whats Sheldon's deal? Is it girls, guys, sock puppets?
Howard: We operate on the assumption that Sheldon has no deal. Though we have many theories about how he might reproduce. I'm an advocate of mitosis.
Penny: What?
Howard: I believe that one day Sheldon will eat an enormous amount of Thai food and spilt into two Sheldons.

Sheldon: Leonard, you may be right. It appears that Penny secretly wants you in her life in a very intimate and carnal fashion.
Leonard: You really think so?
Sheldon: Of course not. Even in my sleep-deprived state, I've managed to pull off another one of my classic pranks. Bazinga!

Sheldon: I often forget other people have limitations. It's so sad.
Howard: He can feel sadness?
Leonard: Not really. It's what you and I would call condescension.