Leonard: What do you mean it happened again?!

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: 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: I'd suggest using some lubricant, but I have a feeling you fell on that as well.
Howard: Not funny, Leonard.
Raj: Really? A robot hand’s got a death grip on your junk, dude. That’s funny, ask anyone.

Althea: What is this?
Howard: It's a robot arm.
Althea: Where's the rest of the robot?
Howard: I only built the arm.
Althea: Because that's all you needed, right?

Sheldon: I am aware of the way humans usually reproduce which is messy, unsanitary and based on living next to you for three years, involves loud and unnecessary appeals to a deity.
Penny: Oh, God.
Sheldon: Yes, exactly.