Sheldon: This is the temperature you agreed to in the roommate agreement.
Leonard: Aw, screw the roommate agreement!
Sheldon: No, you don't screw the roommate agreement. The roommate agreement screws you.

Mrs. Wolowitz Howard, are you having a playdate?
Howard: I don't have playdates. I have colleagues.
Mrs. Wolowitz Do their parents know they're here?
Howard: No, but if you keep screaming, maybe they'll hear you.

Leonard: You know what, go to Hell and set their thermostat.
Sheldon: I don't have to go to Hell. At 73 degrees, I'm there already!

Sheldon: I assure you, you'll be sorry that you wasted your money on an iPod when Microsoft comes out with theirs.
Rajesh: Do you have an opinion about everything?
Sheldon: Yes.
Howard: And you just assume you're right?
Sheldon: It's not an assumption.

Sheldon: When do you evacuate your bowels?
Leonard: When I have to.
Sheldon: When you have to? I'm sorry I don't rent to hippies.

Sheldon: What's the sixth noble gas?
Leonard: Uh, radon?
Sheldon: Are you asking me or telling me?
Leonard: Telling you?
(Sheldon gives Leonard a stern look)
Leonard: Telling you.

Sheldon: Oh, Ubuntu. You're my favorite Linux-based operating system.

Leonard: Can I sleep on your couch tonight?
Penny: Well, you can try. But the neighbors across the hall are being very noisy.
Leonard: Oh, you heard that, huh?
Penny: Yeah, apparently the one fella changed the thermostat, and then the other fella went bat-crap crazy.

Leonard: Not only that Sheldon saved my life, but that he didn't report me to the landlord, or the police, or homeland security.

Leonard: Hey. Excuse me, I'm looking for a Dr. Sheldon Cooper.
Asian Guy: Oh, so you're here about the room?
Leonard: Yeah.
Asian Guy: Run away, dude.
Leonard: Wait. What?
Asian Guy: Run fast, run far!

Penny: Okay, Babydoll Pink, let's see if you can cover up the fact that I got my dad's feet.

TV Announcer: Up next Babylon 5.
(Sheldon looks at Leonard)
(Penny listening to Sheldon and Leonard argue from her apartment)
Leonard: You're not even watching it.
Sheldon: I can hear it.
Leonard: The dialogue offends you?

Leonard: You know what, go to Hell and set their thermostat.
Sheldon: I don't have to go to Hell. At 73 degrees, I'm already there.

Sheldon: And next, if either of us ever invents time travel, we agree our first stop will be this meeting today in precisely five seconds.
Leonard: Okay. [They look around, nothing happens]
Sheldon: Well that's disappointing.

Sheldon: Last question. In a post-apocalyptic world, which task would you assign the highest priority? Locating a sustainable food source, re-establishing a functioning government, procreating, or preserving the knowledge of mankind.
Leonard: Uh, I'm gonna go with preserving the knowledge.
Sheldon: That's correct. FYI, I would have accepted any answer other than procreating.