Leonard: My point is, Priya's gone. And it would be much better if no-one else found out about this.
Sheldon: You mean, you want me to keep a secret?
Leonard: Yes.
Sheldon: You know I can't keep a secret.
Leonard: You can if you try. Think about it this way, if I were Batman and you were Alfred, you'd keep that secret. Right?
Sheldon: Why do you get to be Batman?
Leonard: Because, well, Batman has the secret.
Sheldon: Well Alfred has secrets too.
Leonard: Like what?
Sheldon: Alfred knows that Barbara Gordon is Batgirl. Which I've now just told to Batman. See, I can't keep a secret.

Raj: I don't like bugs, okay. They freak me out.
Sheldon: Interesting. You're afraid of insects and women. Ladybugs must render you catatonic.

Sheldon: Scissors cuts paper, paper covers rock, rock crushes lizard, lizard poisons Spock, Spock smashes scissors, scissors decapitates lizard, lizard eats paper, paper disproves Spock, Spock vaporizes rock, and as it always has, rock crushes scissors.

Sheldon: Why are you crying?
Penny: Because I'm stupid.
Sheldon: That's no reason to cry. One cries because one is sad. For example, I cry because others are stupid, and that makes me sad.

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.

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.