Penny: So, you know, isn't there maybe some way you and Sheldon could compromise on this whole presentation thing?
Leonard: No. Scientists do not compromise. Our minds are trained to synthesize facts and come to inarguable conclusions. Not to mention Sheldon is bat-crap crazy

Wolowitz: I just checked the house. There's probably 20, 25 people in there.
Leonard: You're kidding!
Penny: Is that all?
Leonard: "All?" In particle physics, 25 is Woodstock.

Sheldon [knocking on Penny's door]: Penny, Penny, Penny...
[Penny opens the door]
Sheldon: Good morning.
Penny: Do you have any idea what time it is?
Sheldon: Of course I do, my watch is linked to the atomic clock in Boulder, Colorado. It's accurate to one-tenth of a second, but as I'm saying this it occurs to me once again your question may have been rhetorical

Leonard: Penny, say hello to Leo.
Penny: Hi, Leo. How are you feeling?
"Leo": Have you ever woken up in a flea-bag motel, covered in your own vomit, next to a transsexual prostitute?
Penny: No.
"Leo": Then don't ask me how I'm feeling.

Every family in America has a relative holed up in a garage somewhere huffing paint thinner

Sheldon: Anyway, the housekeeper in the faculty residence didn't speak any English. When I finaly managed to convince her I was sick, she said, "Möchtest du eine Darmspülung?"
Penny: What does that mean?
Sheldon: Based on what happened next, I assume it means, "Would you like an enema?"

[at The Cheesecake Factory]
Penny: Why didn't you just have soup at home?
Sheldon: Penny, I have an IQ of 187. Don't you imagine if there were a way for me to have soup at home, I would have thought of it?
Penny: You can have soup delivered.
Sheldon: I did not think of that

Wolowitz: We need a hot 15-year-old Asian girl with a thing for smart guys.
Penny: What?
Leonard: Howard, that's racist. Any fifteen year old girl will do the trick

Sheldon: In Texas, when a cow stops giving milk, they don't continue feeding her. They take her out and shoot her between the eyes.
Penny: I'm confused. Did Sheldon stop giving milk?

[Raj whispers in Wolowitz's ear]
Penny: What did he say?
Wolowitz: He compared Sheldon to a disposable feminine cleansing product one might use on a summer's eve.
Penny: Yeah, and the bag it came in

Leonard: Sheldon, you have to let somebody else answer.
Sheldon: Why?
Penny: Because it's polite.
Sheldon: What do manners have to do with it? This is war. Were the Romans polite when they salted the ground of Carthage to make sure nothing would ever grow again?

Penny: I'm a Sagittarius, which probably tells you way more than you need to know.
Sheldon: Yes, it tells us that you participate in the mass cultural delusion that the sun's apparent position relative to arbitrarily defined constellations at the time of your birth somehow affects your personality.
Penny: Participate in the what?

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?