Sheldon: Your check-engine light is on.
Penny: Uh huh.
Sheldon: Typically, that's an indicator to, you know, check your engine.
Penny: It's fine. It's been on for like a month.
Sheldon: Well, actually that would be all the more reason to, you know, check your engine.
Penny: Sheldon, it's fine.
Sheldon: If it were fine, the light wouldn't be on. That's why the manufacturer installed that light, to let you know it's not fine.
Penny: Maybe the light's broken.
Sheldon: Is there a check-the-check-engine-light light?

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 14 and had already achieved more than 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. It's more likely that you will spend your careers teaching fifth graders how to make paper-mache volcanoes with baking-soda lava.
Leonard: Oh, good God.
Sheldon: In short, anyone who told you that you would someday be able to make any 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. Now, if you'll excuse me, the latest issue of Batman is out. Come, Leonard.
Leonard: Laser demonstration's looking pretty good now, huh?

Sheldon: Oh God, not Euclid Avenue!

Sheldon: I still don't see why I need a driver's license. Albert Einstein never had a driver's license.
Howard: Yeah, but Albert Einstein didn't make me wet myself at 40 miles an hour.
Penny: Yeah, and I never wanted to kick Albert Einstein in the nuts.

DMV Worker: Here's your learner's permit. Go away.
Sheldon: But I'm not done. I have many additional concerns about these questions.
DMV Worker: Don't make me climb over this counter!

Sheldon: Excuse me, but I have some concerns about these questions.
DMV Worker: Look at that sign up there.
Sheldon: Yes?
DMV Worker: Does it say I give a damn?
Sheldon: No.
DMV Worker: That's because I don't.

Sheldon: (To the cleaning ladies) You saw nothing!

Sheldon: Maybe if I turn off the nightlight, I can keep the sheets.

Leonard: So if you are considering going into experimental physics, my door is always open. Once again, I'm sorry that the demonstration didn't quite work out. But now we know what happens when you accidentally spill peach snapple into a helium-neon laser. The short answer is don't.

Raj: I love this time of the year. The leaves are turning, there's a bracing chill in the air.
Howard: Plus there's a whole new crop of female grad students about to put on just enough winter weight to make them needy and vulnerable. That's right, honey, have another calzone. Daddy can wait.

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: (To Penny) Apparently, I'm in some kind of relationship, and, well, you seem to be an expert at ending them.
Penny: Excuse me?
Sheldon: I see man after man leaving this apartment never to return.
Penny: Okay, first of all, it is not man after man.

Leonard: Sheldon lives in fear of the three-tined forks.
Sheldon: Three tines is not a fork. Three tines is a trident. Forks are for eating, tridents are for ruling the seven seas.

Penny: Look, Sheldon, I'm really, really sorry but it's only going to be for a week. Can't you be a little bit flexible?
[Leonard, Howard, Raj and Sheldon all look at her]
Penny: Yeah, sorry, I didn't really think that through.

Raj: Isn't there a policy against dating graduate students?
Leonard: No, if you can talk to them, you can ask them out.
Raj: Damn, there's always a catch.