It's very simple. 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

Amy: Jewelry? Seriously? Sheldon, you are the most shallow, self-centered person I have ever met. Do you really think that another transparently manipul... Oh! It's a tiara! A tiara. I have a tiara! Put it on me, put it on me, put it on me, put it on me, put it on me, put it on me, put it on me.
Penny: You look beautiful
Amy: Of course I do. I'm a princess and this is my tiara.
Sheldon: You were right, the tiara was too much.

Leonard: Have you considered telling her your feelings?
Sheldon: Leonard, I'm a physicist, not a hippie.
Leonard: Well let me see if I can explain your situation using physics. What would you be if you were attached to another object by an incline plane, wrapped helicly around an axis.
Sheldon: Screwed.
Leonard: There you go.

Would you like some aloe vera? You just got burned.

Raj: We'd just see what's what.
Sheldon: That's a semantically null sentence.

Penny: Not knowing's part of the fun.
Sheldon: Was that the motto of your community college?

I do not have to urinate. I am a master of my own bladder. Drat.

No, Gorn, no! That's where I sit.

Amy: When you told me I was going to be "losing my virginity," I didn't think you meant you'd be showing me Raiders of the Lost Ark for the first time.
Sheldon: My apologies. I chose my words poorly. I should have said you were about to have your world rocked on my couch.

Leonard: When we watch Frosty the Snowman, he roots for the sun.
Sheldon: Excuse me, but the sun is essential for all life on earth. Frosty is merely a bit of frozen, supernatural ephemera in a stolen hat. A crime, by the way, for which he is never brought to account.

Stephen Hawking: You made an arithmetic mistake on page two. It was quite a boner.
Sheldon: No, no ... that can't be right. I-I don't make arithmetic mistakes.
Stephen Hawking: Are you saying I do?
Sheldon: Oh, no, no, no, of course not. It's just, I was thinking.... Oh, gosh, golly, I made a boo-boo and I gave it to Stephen Hawking.
Stephen Hawking: Great, another fainter.

Boldly go, Howard Wolowitz.

TBBT Quotes

Oh, Bernadette, please play my clarinet.

Raj's poem

Sheldon: I'll have a diet Coke.
Penny: Can you please order a cocktail? I need to practice mixing drinks.
Sheldon: Fine... I'll have a virgin Cuba Libre.
Penny: That's... rum and Coke without the rum.
Sheldon: Yes, and would you make it diet?