Sheldon: *Laughs* Very good. Because a gorilla go-go dancer of any sexual preference would be out of place in a film about the Holocaust.
Leonard: It only gets funnier when you explain it, Sheldon.
Sheldon: I know.

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.

Bernadette: Maybe we should get one of those machines to help her up the stairs.
Howard: You mean a forklift?

Leonard: Oh, I know. This might help. *Gets a ring out of his wallet*
Penny: Where did you get a ring?
Leonard: I've had it for a couple of years. Not important. Penny, will you marry me?
Penny: Oh, my God, yes.
Leonard: This would have been so much more romantic if you didn't have monkey hair on your finger.

Bernadette: I'm glad I got that mocha. And you know what else I'm glad about? I bought you a brownie and I ate it in the car!