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: 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

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

Leonard [referring to Sheldon singing]: What got into him?
Penny: Oh, just a couple virgin Cuba Libres that turned out to be kinda slutty

Leonard: Look at the bright side. [Lalita] might turn out to be a nice, beautiful girl.
Raj: Great, then we'll get married, I won't be able to talk to her, and we'll spend the rest of our lives in total silence.
Wolowitz: Worked for my parents

Penny [to Raj about Lalita]: No one can make you get married. Why don't you just meet this girl and see what happens?
Raj: Haven't you been listening to me? I cannot talk to women!
Leonard: Um, Raj?
Wolowitz: No, no, let's see how long it takes him

TBBT Quotes

Penny, there's only one cookie with something in the middle that solves life's problems, and that's an Oreo. Or a Nutter Butter, if you're in a pinch.

Sheldon

Leonard: Hi. I'm Leonard. You are beautiful. You pop, sparkle and buzz electric. I'm going to pick you up at eight, show you a night you will never forget.
Raj: Where are we going?