Some of my favorites..
Spike: It's what Caesar did, and he's not going around saying, 'I came, I conquered, I felt really bad about it!
Xander: Party in my eye socket and everyones invited!
Andrew: In my plan, we are beltless.
Willow: I'm a blood-sucking fiend! Just look at my outfit!
Xander: I laugh in the face of danger. Then I hide until it goes away.
Giles: You have responsibilities that other girls do not.
Buffy: Oh! I know this one! Slaying entails certain sacrifices, blah blah biddy blah, I'm so stuffy, give me a scone.
Spike: This is the crack team that foils my every plan? I am deeply shamed.
Xander: Excuse me, who made you the boss of the group?
Anya: You did.
Tara: You said 'Willow should be boss'.
Anya: And then you said, 'Let's vote' and it was unanimous.
Tara: You made her that little plaque that said, 'Boss of Us', you put on the sparkles-
Xander: Valid points, all.
Xander: For I am Xander, King of Cretins. May all lesser cretins bow before me.
Buffy: Your logic does not resemble our Earth logic.
Buffy: I didn't jump to conclusions. I took a small step, and conclusions there were.
Xander: We're right behind you, only further back..
Anya: I, Anya, promise to...love you, to cherish you, to honor you, uh, but not to obey you, of course, because that's anachronistic and misogynistic and who do you think you are, like a sea captain or something?
Anya: What's she doing? Xander said he was going to dig. I want to see Xander dig.
Buffy: That's part's just ceremonial.
Anya: Well, it bites. She's not rippling at all. Oh. Look, there he goes. Look at him.
Willow: Very...diggy.
Anya: Soon he'll be sweating. I'm imagining having sex with him again.
Buffy: Imaginary Xander is quite the machine.
Xander: Like any of that's enough to fight the dark master...bator.
Buffy: You know we love you right.
Willow: We totally do!
Xander: Oh God, we're gonna die aren't we?