Leonard: I'm sorry.
Raj's sister: Why do you say that?
Leonard: When I'm in bed with a girl, that's just my natural response.

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.

Leonard: Penny. We are made of particles that have existed since the moment the universe began. I like to think those atoms traveled fourteen billion years through time and space to create us, so that we could be together and make each other whole.

Sheldon: This song is never going to stop. Have you ever dealt with something so relentlessly irritating?
Leonard: That's a trick question, right?

Raj: Hands off my sister.
Sheldon: Why would I touch your sister? She's all covered in airplane germs.

Sheldon: And to think, I was about to waste the last of my good haemorrhoid cream on you.

Raj: I can't believe you kissed my sister with moth mouth.
Leonard: Well, I can't believe you'd use Sheldon's toothbrush.
Sheldon: You used my toothbrush?
Raj: Not the brush part. Just the little rubber thing to pick food from my teeth and massage my gums.