The Slayer hunts vampires, Buffy is a slayer, don't tell anyone.

The Harvest

Luke: An offering, Master.
Darla: He's a good one! His blood is pure!
Master: You've tasted it. I'm your... faithful dog. You bring me scraps.

Master: I have waited. For three score years I have waited. While you come and go I am stuck here, here in this house of... worship! My ascension is almost at hand. Pray that when it comes... I'm in a better mood.

Giles: For as long as there have been vampires, there's been the Slayer. One girl in all the world, a Chosen One.
Buffy: He loves doing this part.
Giles: All right. The Slayer hunts vampires, Buffy is a Slayer, don't tell anyone. Well, I think that's all the vampire information you need.

Willow: Uh, this may be the dumb question, but shouldn't we call the police?

Giles: You have no idea where they took Jesse?
Buffy: I looked around, but soon's they got clear of the graveyard, they could have just, voom!
Xander: They can fly?
Buffy: They can drive.
Xander: Oh.

Master: If she is a Slayer, and this boy lives, she'll try to save him.
Luke: I thought you nothing more than a meal, boy. Congratulations. You've just been upgraded. To bait.

Giles: So, all the city plans are just, uh, open to the public?
Willow: Um, well, in a way. I sort of stumbled onto them when I accidentally decrypted the city council's security system.
Xander: Someone's been naughty.

Xander: So, what's the plan? We saddle up, right?
Buffy: There's no 'we,' okay? I'm the Slayer, and you're not.
Xander: I knew you'd throw that back in my face.

Giles: Well, then help me. I've been researching this Harvest affair. It seems to be some sort of preordained massacre. Rivers of blood, Hell on Earth, quite charmless. I'm a bit fuzzy, however, on the details. It may be that you can wrest some information from that dread machine. (At the others' stares) That was a bit, um, British, wasn't it?

Xander: And I, in the meantime, will help by standing around like an idiot.
Willow: Not like an idiot, just... standing.

Xander: This is just too much. I mean, yesterday my life's like, "Uh oh, pop quiz." Today it's "rain of toads."

Buffy: I've got a friend down there. Or at least a potential friend. Do you know what it's like to have a friend? ... That wasn't supposed to be a stumper.

Buffy: Xander, what are you doing here?!
Xander: Something stupid. I followed you.
Buffy: Well, you...
Xander: I couldn't just sit at home and do nothing.
Buffy: I understand. Now, go away!
Xander: No!
Buffy: Xander, you're gonna have to.
Xander: Look, Jesse's my bud, okay? If I can help him out, that's what I gotta do. Besides, it's this or chem class.

Xander: So, what else?
Buffy: What else what?
Xander: For vampire slayage.
Buffy: Oh, fire, beheading, sunlight, holy water, the usual.
Xander: You've done some beheading in your time?
Buffy: Oh, yeah. There was this time I was pinned down by this guy that played left tackle for varsity... Well, at least he used to before he was a vampire... Anyway, he had this really, really thick neck, and all I had was a little, little Exact-O knife... You're not loving this story.
Xander: No, actually, I find it oddly comforting.

Cordelia to Willow: Excuse me? Who gave you permission to exist? Do I horn in on your private discussions? No. Why? Because you're boring.

Jesse: They knew you were gonna come. They said that I... I was the bait.
Xander: Oh, great, now you tell us.

Jesse, now a vampire: I feel good, Xander! I feel strong! I'm connected, man, to everything! I, I can hear the worms in the earth!
Xander: That's a plus.
Jesse: I know what the Master wants. I'll serve his purpose. That means you die. And I feed.
Buffy: Xander, the cross!
Xander: Jesse, man. We're buds, don't you remember?
Jesse: You're like a shadow to me now.
Xander: Then get outta my face.

Xander: I don't like vampires. I'm gonna take a stand and say they're not good.
Buffy: So, Giles! Got anything that can make this day any worse?
Giles: How about the end of the world?
Buffy: Knew I could count on you.

Giles: Yes. The Spanish who first settled here called it "Boca del Infierno." Roughly translated, "Hellmouth." It's a sort of, um, portal between this reality and the next. This vampire hopes to open it.
Buffy: Bring the demons back.
Xander: End of the world.
Willow: But he blew it! Or, I mean, there was an earthquake that swallowed half the town, and him, too.
Giles: You see, opening dimensional portals is a tricky business. Odds are he got himself stuck, rather like a cork in a bottle.
Xander: And this harvest thing is to get him out.

Buffy: Mom, I promise, it is not gonna be like before. But I have to go.
Buffy's Mom: No.
Buffy: Mom?!
Buffy's Mom: The tapes all say I should get used to saying it. No.
Buffy: This is really, really important.
Buffy's Mom: I know. If you don't go out it'll be the end of the world. Everything is life or death when you're a sixteen-year-old girl.

Cordelia: Senior boys are the only way to go. Guys from our grade, forget about it, they're children. Y'know? Like Jesse. Did you see him last night, following me around like a little puppy dog. You just wanna put him to sleep. But senior boys, hmm, they have mystery. They have... What's the word I'm searching for? Cars! I just am not the type to settle. Y'know? It's like when I go shopping. I have to have the most expensive thing. Not because it's expensive, but because it costs more.

Luke: Ladies and Gentlemen! There is no cause for alarm. Actually, there is cause for alarm. It just won't do any good.

Buffy, finding Luke about to feed on Cordelia: Oh, I'm sorry, were you in the middle of something?

Xander: Jesse! I know there's still a part of you in there.
Jesse: Okay... Let's deal with this. Jesse was an excruciating loser who couldn't get a date with anyone in the sighted community! Look at me. I'm a new man!

Willow: Did we win?
Buffy: Well, we averted the apocalypse. I give us points for that.

Giles: We've prevented the Master from freeing himself and opening the mouth of Hell. That's not to say he's going to stop trying. I'd say the fun is just beginning.
Willow: More vampires?
Giles: Not just vampires. The next threat we face may be something quite different.
Buffy: I can hardly wait!
Giles: We're at the center of a mystical convergence here. We may, in fact, stand between the Earth and its total destruction.
Buffy: Well, I gotta look on the bright side. Maybe I can still get kicked out of school!
Xander: Oh, yeah, that's a plan. 'Cause lots of schools aren't on Hellmouths.
Willow: Maybe you could blow something up. They're really strict about that.
Buffy: I was thinking of a more subtle approach, y'know, like excessive not studying.
Giles, to himself: The Earth is doomed!