"Gobo, if they're arguing, why are they hugging?"
"Well, Wembley-- uh, I'll ask them."
My vote is a tie between:
1) All Boober's arguments with Sidebottom in "Boober's Quiet Day".
2) Convincing John (as the Vanguard) constantly interrupting Mokey in "The Secret Society of Poohbahs":
"WAAAAAIT!!! She cannot deliver her speech until Mokey has introduced her."
"Oh, all right... Um, this is my good friend Red--"
"WAAAAAIT!!! You cannot introduce a speech in Oopidad unless you are speaking Uffafluff!"
"Uffafluff?"
"That's ightruffafluff!"
"Oh, yes... Um, isthuffafluff isuffafluff ymuffafluff--"
"WAAAAAIT!!! You cannot speak uffafluff unless you are standing on one foot and twirling around on tippietoe and flapping your arms and hiccuping!"
"Isthuffafluff isuffafluff ymuffafluff--"
"WAAAAAIT!!! You forgot to hiccup! And therefore your friend Red Fraggle gets the Ordeal of the Glumberglotts!"
"No! No, please, you can't do that to my friend! She didn't do anything wrong! It was all my--"
"SILENCE!!! Do you have any IDEA what a Fraggle must DO in the Ordeal of the Glumberglotts?"
"Um, uh... No."
"She must wear... FUNNY NOSE GLASSES!!!"
"What?"
"And furthermore... She must juggle okrah soup!"
I love how Convincing John always wiggles his fingers when he says "the Ordeal of the Glumberglotts".