The script for Conversations with Dead People mentioned The First Evil by name, even though it was not yet mentioned in the actual dialogue of the show.

A stage direction in the script for Bring on the Night was:
NOTE: It is VERY important that Giles does not touch or be touched by anything. He can walk and talk - but he can’t fiddle or cuddle or caress. Got it?

The following line was cut from the episode Showtime:
The First (as Eve): “And Chloe, honey… you don’t have to worry about getting called to be the Slayer before you’re ready. You’ll be dead before that happens. All o’you.”

A line of Kennedy’s, referring to the large number of people in the kitchen, was deleted from the episode Potential:
Kennedy: “Hey guys, we fit three more people in here and we can call the Guinness Book people.”

The following lines were cut from the episode The Killer in Me:
Giles: “Well, thank goodness I needn’t worry myself with the idea of bad things happening in my absence. You getting shot, for example. Or throwing everyone in the basement and trying to kill them. Or Willow turning evil…”
Dawn: …

In Beauty and the Beasts, when Xander comes to relieve Willow on “Oz watch”, she explains that Werewolf Oz is more managable on the “second night”, but on the “third night…the real full moon” he is even more “wolf-y”. The problem with that is that the three nights of …

In Into the Woods when Riley comes and stakes Spike with the plastic woodgrain stake, as he turns to leave and Spike begins laughing, when he says “Oh, man”, his American accent slips through and you can distinctly tell. Then he’s back into his English accent again.

In Earshot, when Giles and Wesley are talking about the demon heart needed to cure Buffy’s telepathy, Giles says, “Who’s going to get the demon heart? Berk!” The word Berk (Berkeley Hunt) is Cockney rhyming slang for ‘cunt’.

In the Angel episode ‘Disharmony‘, vampire Harmony goes to L.A. to find her old school friend Cordelia after she’s dumped by Spike. Willow and Cordelia talk on the phone about Harmony - where Willow reveals that Harmony is actually a vampire, and not a lesbian as Cordy believes:

Cordelia: “How come …

In the episode Lie to Me, Angel gets jealous when he sees Ford and Buffy at the Bronze. Buffy says that the Bronze is too crowded and leaves with Ford. Xander then says in a sarcastic way: “Once more, with tension.” The musical episode in season 6 was called Once …

This line of Anya’s was deleted from Empty Places:
“Andrew’s got plenty of tears left in him. Just tell him they cancelled Stargate.”

This conversation between Spike and Andrew was deleted from the episode Empty Places:
Andrew: “This one time, when I was in Sunday school, I woke up late, so my mom made me skip breakfast and I was really hungry, so I told the teacher I had to go to the bathroom, …

The following line was deleted from the scene in End of Days where Willow and Giles try to find out what the scythe is:
Willow: “It doesn’t have any markings. Would it be so hard to include a little sticker? ‘Hello. My name is Blank of the Blankthuselah, consult operating instructions …

The following scene showing Dawn telling the potential Slayers a story was deleted from Chosen:
Dawn: “And the Master grabbed Buffy from behind and bit her. She tried to move, but he was too strong. He fed on her blood and tossed her in the water, cackling insanely as the bubbles …

This speech of Adam’s was deleted from Who Are You?:
“You are here to be my first. To let them know I’m coming. I am the end of all life, of all magic. I’m the war between man and demon, the war that no one can win. You’re a part of …