What's the funniest line from the show?

What about the sexual innuendos ? 

OMWF:

Buffy: What else would I pump you for ?

Buffy: ... I really just said that, didnt I ?

Buffy: Okay, you get fang, I get horny !

Bufffy: ... I mean ...

OMG -- so many candidates, who can choose?

Some of my favorites:

Zeppo:

Xander: You're in a band. That's like a business-class ticket to cool with complimentary mojo after take-off. I gotta learn an instrument. Is it hard to play guitar?
Oz: Not the way I play it.

Xander: You know Oz, I look at all this beauty, all these healthy young women and I wonder why I wasted my time on Cordelia. I mean, look at her. She’s no better lookin’ than the rest of them.
Oz: None of them are really mine...
Xander: Oh my God! He’s lookin’ at her. He’s got his filthy adult Pierce Brosnany eyes all over my Cordy.
Oz: You’re a very complex man, aren’t you.

Oz: Dingoes Ate My Baby played their instruments as if they had plump polish sausages taped to their fingers.
Freddy: Sorry man.
Oz: No, it’s fair.

Willow: OK, say that I help, and you start a conversation, it goes great, you like Buffy, she likes you, you spend time together, feelings grow deeper, and one day, without even realizing it, you find you're in love. Time stops, and it feels like the whole world is made for you two, and you two alone, until the day one of you leaves and rips the still-beating heart from the other, who's now a broken, hollow mockery of the human condition.
Riley: Yep, that's the plan.

Willow: Maybe you're trying too hard. Doesn't this happen to every vampire?
Spike: Not to me, it doesn't!

Xander: Dammit! You know what? I'm sick of this crap. I'm sick of being the guy who eats insects and gets the funny syphilis. As of this moment, it's over. I'm finished being everybody's butt monkey!
Buffy: Check. No more butt monkey.

Buffy: I'm standing right here.

Xander: Spike sang a wittle song?
Anya: Would you say it was a breakaway pop hit or more of a book number?
Xander: Let it go, sweetie.

Sweet: What if I kill you?
Buffy: Trust me. Won't help.

Spike: Oh, listen to Mary Poppins. He's got his crust all stiff and upper with that nancy-boy accent. You Englishmen are always so... Bloody hell! Sodding, blimey, shagging, knickers, bollocks, oh God! I'm English!
Giles: Welcome to the nancy tribe.

Buffy: Hi. How've you been?
Amy: Rat. You?
Buffy: Dead.
Amy: Oh.

Dawn: I know: You never know what's coming. The stake is not the power. To Serve Man is a cookbook. I love you. Go away.

Dawn: So the principal's evil?
Buffy: Or in a boatload of danger.
Xander: Well, the last two principals were eaten. Who'd even apply for that job?

Another great ending:

Willow: It's okay. I understand you having to bail. I can forgive that. Mm, I have to make allowances for what you're going through a-and be a grownup about it. (gives Buffy a slightly smug look)

Buffy: (smiles) You're really enjoying this whole moral superiority thing, aren't you?

Willow: (smiles) It's like a drug!

Buffy: Fine! Okay. I'm the bad. I can take my lumps . . . for a while.

Willow: All right. I'll stop giving you a hard time. (pauses) Runaway !

Buffy: (gives her a surprised look) Will!

Willow: (smiles and giggles) I'm sorry! Quitter !

Buffy: (widens her eyes at her) Whiner !

Willow: Bailer !

Buffy: Harpy !

Willow: Delinquent !

Buffy: Tramp !

Willow: (takes mock offense) Bad seed !

Buffy: Witch !

Willow: Freak !

Cordelia: Is Mr. I'm-the-lead-singer-I'm-so-great-I-don't-have-to-show-
Oz: Yeah, y'know, he's just going by 'Devon' now.

Buffy: I went to Angel's last night and Faith was there. They looked
sort of intimate.
Willow: No way. I know what you're thinking and no way!
Buffy: You're right. Faith would never do that.
Willow: Faith would totally do that. Faith was built to do that.
She's the do that girl.
Buffy: Comfort, remember comfort, here?
Willow: I mean, please, does Angel come up to Faith's standards for
a guy? Let's see, is he breathing?
Buffy: Actually, no.

Giles at the end of The Harvest "The Earth is doomed."
Giles in Chosen "The Earth is definitely doomed."

Spike in Doomed "What's this? Sitting around watching the telly while there's evil still afoot? It's not very industrious of you. I say, we go out there, and kick a little demon ass. What, can't go without your Buffy? Is that it? Too chicken? Let's find her. She is the Chosen One, after all. Come on! Vampires! Grrr! Nasty. Let's annihilate them. For justice, and for the safety of puppies, and Christmas, right? Let's fight that evil. Let's kill something. Oh, come on!"

XANDER: Man, words cannot express how much I hate this place.
GILES: It's dreadful.
ANYA: It's like communism.

GILES: Punishing yourself like this is pointless.
BUFFY: It's entirely pointy.

WILLOW: Say, you all didn't happen to do a bunch of drugs, did ya?

XANDER: Brace yourself. You're not gonna believe it.
TARA: Everyone, before we jump all over her, people do strange things when someone they love dies. When I lost my mother, I-I did some pretty dumb stuff, like lying to my family and staying out all night.
ANYA: Buffy's boinking Spike.

Xander nods. Willow and Tara look surprised.

WILLOW: (pause) Oh ... well, Ta-Tara's right. Grief can be powerful, and we shouldn't judge-
TARA: What are you, kidding? She's nuts!

GILES: 'Do you like my mask? Isn't it pretty? It raises the *dead*!' Americans.

ANYA: For God's sakes, Andrew. You've been in here for 30 minutes. What are you doing?
ANDREW: Entertaining and educating.
ANYA: Why can't you just masturbate like the rest of us?

ANYA: Piano!
XANDER: Because that's what we used to kill that big demon that one time!

Buffy turns to look at them with a confused frown.

XANDER: No wait, that-that was a rocket launcher. (turns to Anya) Ahn, what are you talking about?
ANYA: We should drop a piano on her. Well, it always works for that creepy cartoon rabbit when he's running from that nice man with the speech impediment.
GILES: (rolls his eyes) Yes, or perhaps we could paint a convincing tunnel on the side of a mountain.

XANDER: Just give it time, Ahn. This is hard for all of us. Just ... be patient.
ANYA: I *was* being patient, but it took too long.

GILES: I have a friend who's coming to town
and I'd like us to be alone.
ANYA: Oh, you mean an orgasm friend?
GILES: Yes, that's exactly the most appalling thing you could have said.

BUFFY: If I'm the one who let you die, why take it out on her? I'm right here. C'mon, what're you after? Fear? Revenge? Tasty brains?
DEAD NERD: I think I'd like Dawn to be my girlfriend.
BUFFY: Again, wrong sister. I'm the one that dates dead guys. And, no offense, but they were hotties.

CORDELIA: Hi, Mr. Beech! I was just wondering, were you planning on killing a bunch of people tomorrow? Oh, it's for the yearbook!

DAWN: Anchovies, anchovies, you're so delicious. I love you more than all the other fishes.

BUFFY: Snyder, you alive in there?
SYNDER: You. All of you. Why couldn't you be dealing drugs like normal people?

BUFFY: What is this?
WILLOW: A doodle. I do doodle. You, too. You do doodle, too.

COACH MARIN: Boy, when they were handin' out school spirit, you didn't even stand in line, did you?
BUFFY: No. I was in the line for shred of sanity.

CORDELIA: That is such a twinkie defense. Shylock should get over himself. People who think their problems are so huge craze me. Like this time I sort of ran over this girl on her bike. It was the most traumatizing event of *my* life, and she's trying to make it about *her* leg! Like *my* pain meant nothing.

CORDELIA: You're really campaigning for bitch-of-the-year, aren't you?
BUFFY: As defending champion, you nervous?

MAYOR: So what are kids reading nowadays?

He reaches for an open book -- as Buffy silently conceals the newspaper, eyes never leaving the Mayor.

MAYOR: (reads chapter heading) "The Beast will walk upon the Earth, and Darkness will follow. The several races of man will be as one in their terror and destruction", say, that's kind of sweet, different races coming together...

MASTER: You were destined to die! It was written!
BUFFY: What can I say? I flunked the written.

CALEB: Stupid girl. You'll never stop me. You don't have the b --

As he is saying it, she arcs the blade back and swings it up right between his legs. We don't see it connect, of course, but we sure as hell see his expression when it does.

BUFFY: Well, who does nowadays?

A moment, and she uses both hands to RIP the blade upwards. We see nothing of the damage, but some dark blood spatters her face as she completes the scythe's arc upward. A moment, and we hear the body fall to one side of her -- then hear the other half fall to the other side.
Angel stands, spinning, furious.

ANGEL: Okay, now I'm pissed. Where is he?

Buffy indicates the floor to her left. Angel looks. Then she indicates the floor to her right. Angel looks, then back at her, impressed. Buffy smiles girlishly.

BUFFY: He had to split.

I also really love the "Apathy On The Rise. Nobody Cares" headline from the school newspaper. 

---
A gentleman will not insult me, and no man not a gentleman can insult me.

Buffy says 'wanna see my impression of Ghandi?' And beats a demon to death. 'Ghandi?' The othe girl says, and Buffy replies 'well, you know, if he was really pissed.'

Also when the captain of the football team says they should do all right 'as long there aren't too many mysterious deaths this year.'