Sheldon: I need to know exactly what Leonard did to get you to put an emotional cap in his buttocks.
Penny: What?
Sheldon: Again, urban slang, in which I'm beginning to get remarkable fluency

Penny: Sheldon, what do you want?
Sheldon: I'm certain this will come as no surprise to you, but Leonard is failing in yet another relationship.
Penny: He's having problems with Stephanie?
Sheldon: She's sending virtual livestock to random men on the Internet

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

I believe the appropriate metaphor here involves a river of excrement and a Native American water vessel without any means of propulsion

I am not going to watch the Clone Wars TV series until I've seen the Clone Wars movie. I prefer to let George Lucas disappoint me in the order he intended

Raj: I'll tell you what, how about we go rock-paper-scissors?
Sheldon: Eww, I don't think so. Anecdotal evidence suggests that in the game of rock-paper-scissors, players familiar with each other tie 75-80% of the time due to the limited number of outcomes. I suggest "rock-paper-scissors-lizard-Spock"

I trusted you with my e-mail address, and you betrayed that trust by sending me Internet banality.

Penny: Wait, Sheldon. This has gotten way out of hand. Okay, I've done some stupid things; you've done some stupid things. How about we just call it even and move on with our lives?
Sheldon: I've done no stupid things.
Penny: Look, you've got to meet me half way here.
Sheldon: I am meeting you half-way. I'm willing to concede that you've done some stupid things

Leonard: Put it on the agenda.
Sheldon: You have to make a motion to put it on the agenda.
Leonard: Oh, I'll make a motion, but you're not going to like it

Sheldon: The entire nation dedicated a decade of effort and treasure to put a man on the moon.
Wolowitz: Well, my fellow Americans, before this year is out we will put a Wolowitz on one of America's top models.
Raj: And a large number of people will believe it never happened

Ramona: You're not going to Halo night
Sheldon: Yes, I am. It's Wednesday. Wednesday's Halo night.
Ramona: Didn't a great man once say, "Science demands nothing less than the fervent and unconditional dedication of our entire lives"?
Sheldon: He did.
Ramona: And who was that great man?
Sheldon: Me. Sorry, Leonard.
Leonard: Seriously? You're not coming?
Sheldon: You heard her. How can I argue with me?

Sheldon: Looking out at your fresh young faces, I remember when I, too, was deciding my academic future as a lowly graduate student. Of course, I was fourteen. And I had already achieved more than most of you could ever hope to, despite my 9:00 bedtime. Now, there may be one or two of you in this room who has what it takes to succeed in theoretical physics, although it's more likely that you'll spend your scientific careers teaching fifth graders how to make papier-mâché volcanoes with baking soda lava.
Leonard: Oh, good God.
Sheldon: In short, anyone who told you that you would someday be able to make some significant contribution to physics, played a cruel trick on you—a cruel trick indeed. Any questions? ... Of course not. I weep for the future of science

TBBT Quotes

What do Sheldon Cooper and the black hole have in common? They both suck.

Professor Hawking

Raj: Okay, here's another one: if a zombie bites a vampire, and the vampire bites a human, does the human become a vampire or a zombie? Or, a zompire?