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?"

If influenza was only contagious after symptoms appear, it would have died out thousands of years ago. Somewhere between tool using and cave painting, Homo habilis would have figured out to kill the guy with the runny nose

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

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: 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

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

Leonard [watching their fight on YouTube]: Oh, geez, does this suit really look that bad?
Sheldon: Forget your suit. Look at my arms flailing. I'm like a flamingo on Ritalin

Leonard: Sheldon, why is this letter in the trash?
Sheldon: Well, there's always the possibility that a trash can spontaneously formed around the letter, but Occam's Razor would suggest that someone threw it out

Leonard: You are not Isaac Newton.
Sheldon: No, no, that's true. Gravity would have been apparent to me without the apple

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?