Sheldon: Oh, come on, you can't tell me that you're not intrigued about the possibility of building a better girlfriend.
Leonard: I'm not. And Penny's qualities, both good and bad, are what make her who she is.
Sheldon: You mean, like that high-pitched, irritating laugh?
Leonard: Yes.
Sheldon You wouldn't prefer a throaty chuckle?
Leonard: You're not changing how Penny laughs.
Sheldon: No, that would be incongruous, I was going to lower the whole voice to a more pleasing register.

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.

Penny: I give up. He's impossible.
Sheldon: I can't be impossible; I exist. I think what you meant to say is, 'I give up; he's improbable'.

Sheldon: You know, I've always wanted to go to a goth nightclub.
Howard: Really?
Sheldon: Bazinga! You never see any of my practical jokes coming, do you?

Leonard: I'm just saying, you catch more flies with honey than with vinegar.
Sheldon: You catch even more with manure, what's your point?