Leonard: We're going to Long Beach?
Sheldon: No, of course not. There's no Cousin Leo; there's no intervention. Focus, Leonard.
Leonard: Oh, come on.
Sheldon: We just leave the house on Friday night, and we return in the wee hours, emotionally wrung out from the work of convincing Leo to go back into rehab.
Leonard: So, he goes back into rehab?
Sheldon: Yes, but he can relapse if Penny ever invites us to hear her sing again

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

Penny

Leonard: Sheldon, are you worried about your safety?
Sheldon: No, I imagine if you were going to kill me, you'd have done it a long time ago.
Leonard: That's very true

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.

Leonard: How long is [Leo] going to stay here?
Sheldon: He's a homeless drug addict, Leonard. Where's he going to go? Boy, you have a lot to learn about lying

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

Sheldon: I'm uncomfortable having been included in your lie to Penny.
Leonard: What was I supposed to say?
Sheldon: You could have told her the truth.
Leonard: That would have hurt her feelings.
Sheldon: Is that a relevant factor?
Leonard: Yes.
Sheldon: Then I suppose you could have agreed to go.
Leonard: And what would I have said afterwards?
Sheldon: I would suggest something to the effect of, 'singing is neither an appropriate vocation nor avocation for you, and if you disagree I'd recommend you have a CAT scan to look for a tumor pressing on the cognitive processing centers of your brain

Leonard: Sheldon, we have to do this.
Sheldon: No, we don't. We have to take in nourishment, expel waste, and inhale enough oxygen to keep our cells from dying. Everything else is optional

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.

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

Howard, would you like to explain to me why your Facebook page has a photo of me sleeping on your shoulder captioned, "Me and My Girlfriend?"

Penny

Leonard: Are there any other honors that I've gotten that I don't know about? Did UPS drop off a Nobel Prize with my name on it?
Sheldon: Leonard, please don't take this the wrong way, but the day you win a Nobel Prize is the day I begin my research on the drag co-efficient of tassels on flying carpets

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?