Sheldon: Who do I speak to about permanently reserving this table?
Penny: I don't know, a psychiatrist?

Leonard: If Penny didn't know that Leslie had already turned me down then that would unambiguously mean that she, Penny, thought I should ask her, Leslie, out, indicating that she, Penny, had no interest in me asking her, Penny, out but because she did know that I had asked Leslie out and that she, Leslie, had turned me down then she, Penny, could be offering me consolation. "That's too bad, you would have made a cute couple" but while thinking "good, Leonard remains available."
Sheldon: You're a lucky man Leonard.
Leonard: How so?
Sheldon: You're talking to one of three men in the western hemisphere capable of following that train of thought.
Leonard: Well, what do you think?
Sheldon: I said I could follow it, I didn't say I cared.

Sheldon: I don't know what the protocol is here. Do I stay, do I leave? Do I wait to greet them with a refreshing beverage?
Penny: Gee, Sheldon, you're asking the wrong girl. I'm usually on the other side of the tie.

Leonard: Leslie, this is Penny, she lives across the hall from Sheldon and me.
Howard: ... And walks in quiet beauty like the night.
Penny: Howard, I asked you not to do that.

Sheldon: I need your help in a matter of semiotics.
Penny: What?
Sheldon: Semiotics, the study of signs and symbols as a branch of the philosophy related to linguistics.
Penny: Okay, honey, I know you think you are explaining yourself, but you're really not.

Leslie: Listen Leonard, neither of us are neuro-scientists, but we both understand the bio-chemistry of sex, ... I mean: Dopamine in our brain is released across synapses causing pleasure. You stick electrodes in a rat's brain, give him an orgasm button and he'll push that thing 'till he starves to death.
Leonard: Who wouldn't?

Sheldon: My equations, someone's tampered with my equations.
Leonard: Are you sure?
Sheldon: Of course I'm sure. Look at the beta function of quantum chromodynamics. The sign's been changed.
Leonard: Oh, yeah. But doesn't that fix the problem you've been having?
Sheldon: Are you insane? Are you out of your mind? (looking at board) Are you--? Hey, look, that fixes the problem I've been having.

Sheldon: Can't we just go to Big Boy? They only have one burger: the Big Boy.
Penny: The Barbecue Burger is like the Big Boy.
Sheldon: Excuse me, in a world that already includes a Big Boy, why would I settle for something that's like a Big Boy?

Leslie: Come for the breasts, stay for the brains!

Sheldon: Waitresses don't yell at you at Big Boy.

Penny: Leonard's had girls over before, right?
Sheldon: Oh, yes, but there's usually planning, courtship and advance notice. Last time I was able to book a cruise to the Arctic to see a solar eclipse.
Penny: Wait, you had to leave the state because your roommate was having sex?
Sheldon: I didn't have to, the dates just happened to coincide.

Sheldon: I don't come into your house and touch your board.
Leslie: There are no incorrect equations on my board.
Sheldon: Oh, that is so... so...
Leslie: I'm sorry, I've got to run. If you come up with an adjective, text me.

Leslie: Oh, Leonard, you magnificent beast.

Leslie: I didn't know you eat here.
Sheldon: We don't, this is a disturbing aberration.

Leslie: Just so we're clear, you understand that me hanging back to practise with you is a pretext for letting you know that I'm sexually available.
Leonard: Really?
Leslie: Yeah, I'm good to go.
Leonard: I thought you weren't interested in me.
Leslie: That was before I saw you handling that beautiful piece of wood between your legs.
Leonard: You mean my cello?
Leslie: No, I mean the obvious crude double entendre. I'm seducing you.