Sheldon: Well, I would love to help you, but since I discovered the satisfaction of working with my hands on a train engine, I don't think I can go back to theory. I'm an engineer now. And, hey, just to be clear, a train engineer. Not that goofy kind you are.

Leonard: Come on, Sheldon. You can't turn your back on physics. Besides, you have no idea what you're doing with this stuff.
Howard: But if you really want to learn the mechanical side, I can teach you anything you want to know.
Leonard: And instead of standing around watching, you can help us build your smaller guidance system.
Howard: And with all these new skills, you'd be able to fix any model train. You'd be the king of the train store!
Sheldon: Excuse me. I have a girlfriend. I'm already king of the train store.

Amy: The food here's supposed to be great. Don't fill up on chips.
Sheldon: Oh, I won't. I have a trick. I only eat equilateral triangles. Isosceles, isosceles, oh, scalene (breaks the corner off a chip and eats it) - You didn't see that.

Amy: You know about that?
Bert: Uh, yeah, everyone at the university does.
Amy: Were you aware of this?
Sheldon: No. No, I only told Leonard, Howard, Raj, Kripke, uh, Professor Wu, Professor Klein, and a lunch lady in the cafeteria. How everyone else found out is a mystery to me.

Amy: Are you really worried about revealing secrets to Stephen Hawking?
Sheldon: No, I was just excited to list him as a friend.

Sheldon: Excuse me. May I have your attention, please? I have recently been made aware that my personal relationship with Amy Farrah Fowler has become water cooler gossip. And I just want to say, shame on all of you. We're scientists. Our minds should be focused on the advancement of human knowledge, not the intimate details of other people's lives.
Bert: He's right. And I'm sorry for the part I played in this.
Sheldon: Thank you, Bert. You're a good man. That woman who stood you up and humiliated you last night really missed out.
Bert: That doesn't paint me in the best light.
Sheldon: Uh. Oh, I'm sorry. Correction: That woman not only had vigorous coitus with Bert, she also tipped him a dollar for a job well done. That better?
Bert: Not really.

Sheldon: All right, well, to sum up: Focus on science, keep your nose out of other people's business, and, uh, whoa, for a good time, call Bert.

Leonard: What brought that on?
Sheldon: (sighs) Well, last night Amy was angry with me because I'd been foolishly telling people about certain personal matters.
Howard: That's understandable.
Sheldon: Oh, I know that now. At first, I thought she was cranky because of her horrific menstrual cramps. It turns out, no, she was genuinely mortified.

Raj: How bad is it?
Sheldon: Let me put it this way. Do you own a barrel and suspenders?
Raj: Are you serious?
Sheldon: I'm not wearing this visor to play women's golf.

Raj: Go ahead, make jokes. I don't know why you think you're going to Comic-Con. You just had a baby.
Howard: So?
Raj: Well, so? So you think Bernadette's just gonna let you jet down to San Diego for five days and leave her alone?
Leonard: Hang on. So I have to bring Penny, you can't afford it, Howard's gonna get in trouble, and this guy gets to have a great time.
Sheldon: I'm gonna go as Dumbledore.

Sheldon: I can't wait to tell them.
Amy: No, you're not gonna tell them anything. You're gonna stay out of it.
Sheldon: Why?
Amy: Because it's between them.
Sheldon: Well, if you haven't noticed, I've been between them for the last ten years.

Bernadette: Keep it. Consider it a gift.
Sheldon: Hold on. Is it back pay or is it a gift?
Bernadette: What's the difference?
Sheldon: When the IRS questions us in separate rooms, we need to have our stories straight.

Amy: For the last time, no Hulk, no Batman, no life-size statues.
Sheldon: Wow. I'm starting to think you didn't mean it when you said you wanted to spruce up the place.

Sheldon: I mean, it's unfair. People just assume I'm going to be upset by Raj moving into my old room.
Amy: But you are, aren't you?
Sheldon: Oh, I'm outraged.

Amy: Talk to me. Tell me what's going on.
Sheldon: Well, that's been my room since before I met Leonard, and now someone else is going to be living in it. And that someone else is not me. And you know how I feel about people who aren't me.