Sheldon: Penny, if I'm going to get Leonard a gift, I'm going to do it right. I refuse to let him experience the same childhood trauma I did.
Penny: I know I'm gonna regret this, but what trauma?
Sheldon: On my 12th birthday, I really wanted a titanium centrifuge so, you know, I could separate radioactive isotopes.
Penny: Of course, yeah.
Sheldon: Instead of a titanium centrifuge, my parents bought me-- Wow, this is hard. They got me a motorized dirt bike.
Penny: No!
Sheldon: What 12-year-old boy wants a motorized dirt bike?
Penny: All of them.

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.

Howard: Try telling him it's a non-optional social convention.
Penny: What?
Howard: Just do it!
Penny: It's a non-optional social convention.
Sheldon: Oh, fair enough.
Howard: He came with a manual.

Sheldon: What computer do you have? And please don't say a white one.

Store Clerk: Excuse me, Sir, you don't work here.
Sheldon: Yes, well apparently neither does anyone else.