Harmony; So, Slayer. At last we meet. Buffy: We’ve met, Harmony, you half-wit.
However, the funnies moment is non-verbal.
In “Dopplegangland” the group think Willow has been vamped. When Willow enters the library everybody jumps to their feet. Xander brandishes a cross to the non-vamped Will. When it has no effect, he shakes the cross to get it working and brandishes it again.
Dawn: Oh, my god. You will never believe what happened at school today. Buffy: Everybody started singing and dancing? Dawn: I gave birth to a pterodactyl. Anya: Oh my god, did it sing?
All of Smile Time. Spike: [Counting on his fingers] Sodding, blimey, shaggin’, knickers, bollocks. Oh, God. I’m English.
The single funniest moment in the Whedonverse is an outtake from Serenity, available on the DVD:
Mal: “String up some bodies, four or five should do, and make sure Shepard Book is at the front, he was our friend and we should honour him. Kaylee, I want you to get the kid takin’ a dirt nap with baby Jesus, we need a hood ornament, and Jayne, try not to steal too much of their shit.”
Wash: This sounds like something from Science Fiction.
Zoë: Honey, we live in a space ship.
and
Anya: How can I help?
Willow: Uh, distract him from Buffy. Uh, piss him off.
Anya: I don’t know how!
Willow: Anya, I have faith in you. There is no one you cannot piss off.
close up on Xander, apparently reviewing a battle plan; pull back to reveal a game of D & D, a scene which contains one of my favorite lines:
Giles: “I used to be a highly respected Watcher. Now, I’m a wounded dwarf with the mystical strength of a doily.”
eta: Giles has been demonized by Ethan; Giles and Spike are on their way to find Ethan (or possibly Buffy); Giles spies Maggie Walsh from the car, tells Spike to pull over, gets out, chases Maggie; satisfied, he gets back in the car and they continue on.
I don’t know Buffy etc., but the funniest lines in Firefly were all ones that weren’t spoken.
In the pilot episode, when Mal discovers the Alliance mole. No dramatic speeches, just bang.
In “The Train Job”, Mal kicking the thug into the engine.
And in the movie, River’s raised eyebrow in response to “Am I talking to Miranda right now?”.