Penny: This is just to give you ideas. You know, do-do you want something simple and elegant? I mean, do you want a train?
Sheldon: [entering the apartment] Ooh, we're talking about trains.
Amy: Not the kind of trains you like.
Sheldon: Oh, I like all kinds of trains: steam, diesel, coal, elevated, bullet. I defy you to name a train that I don't like.
Penny: The kind on the back of a wedding dress?
Sheldon: I did not see that coming. Good job.

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.

Sheldon: Wow! You look beautiful.
Amy: Really? 'Cause I was gonna return it.
Sheldon: Why would you return it? You look like a pile of swans.

Penny: What if you asked for $20 million?
Sheldon: I'm sorry, I'm trying to do science, not hire Lady Gaga to come to my birthday.
Penny: Do you even know who Lady Gaga is?
Sheldon: Presumably, the wife of Lord Gaga.

Sheldon: But I need it. It's the only way to settle the contradictions between gravity and quantum mechanics.
Penny: Well, it's too much money, you can't ask for that all at once.
Sheldon: Well, what if I ask for it in six easy installments of $83,333,333.33?