What Anne said.

Some BtVS "three" quotes:

Buffy: Cordelia, I have at least three lives to contend with, none of which really mesh. It's kind of like oil and water and a... third unmeshable thing.

Willow: Well, I like you. You're nice and you're funny. And you don't smoke. Yeah, okay, werewolf, but that's not all the time. I mean, three days out of the month I'm not much fun to be around either.

Whistler: Right now, you couldn't go three rounds with a fruit fly!

Cordelia: I ran. I think I made it through three counties before I realized nobody was chasing me. Not too brave.

Buffy: The girl's not playing with a full deck, Giles. She has almost no deck. She has a three.

Buffy: The count of three isn't a plan. It's Sesame Street.

Wesley: Remember the three key words for any Slayer: preparation... preparation... preparation.
Buffy: That's one word three times.

Oz: Well, other bands know more than three chords. Your professional bands can play up to six, sometimes seven *completely* different chords.

Buffy: Oh come on! What am I, Saint Buffy? He's like three feet tall!

Buffy backs up a step: ?Pain, - death, - apocalypse. - None of it fun. - Do you know what a Hellmouth is? Do you have a fancy term for it? Because I went to high school on it, for three years.

Anya: Come on, somebody bet already. I got three 'K' cards.

XANDER: No, we're not going to (in Dracula's accent) "leave you." And where'd you get that accent, Sesame Street? (As the Count on Sesame Street) Vun, two, three -- three victims. Mwa ha ha!

Anya: Like there were only three walls and not a fourth wall and

Willow: Uh, Amy ... three things we have to talk about. One, Larry's gay. Two, Larry's dead. And three, high school's... kinda over.

Exactly. (eta: On the dead twice thing, hence third time a slayer)

I always liked the "on the count of three is not a plan" line too.

Buffy 3: Once, twice, three times a slayer.

This. I would take out "She's".

I also like that one, but perhaps it should be

Unce, Dice, Fwree Times a Mady

Alfalfa would be happy to know he was remembered.

I still vote "once, twice, three times..." but I have to mention my love for each of these quotes:

Buffy: The girl's not playing with a full deck, Giles. She has almost no deck. She has a three.

Buffy: The count of three isn't a plan. It's Sesame Street.

Buffy 3: She's once, twice, three times a slayer.

I like.

Buffy 3: Once, Twice, Three Times a Slayer

I like. Might just end up as the penultimate thread for the season or even the series.

Buffy: The girl's not playing with a full deck, Giles. She has almost no deck. She has a three. Buffy: The count of three isn't a plan. It's Sesame Street. Buffy 3: She's once, twice, three times a slayer.

I like these three -- maybe "once, twice, three times" a smidge more.

Buffy 3: She's once, twice, three times a slayer.

I like this, but am I the only one trembling in fear at the thought of X weeks of a Lionel earworm?

We'll have it with some overlap with "No Time for Losers" and "I forget what 8 was for," so it'll just be duelling earworms.

Or not, depending on which of the songs you know.