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

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.

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.