Susan and Fred debating the existence of giants while watching a balloon of a giant baseball player float by during the parade.
Susan: Sometimes people grow very large, but that's abnormal.
When Susan asks Doris what happened to the man previously hired to play Santa in the parade, Doris asks her if she remembers the drunken janitor from a New Year's Eve party. Susan says she does, so Doris tells her she found the parade performer in an even worse condition.
When Doris Walker is trying to convince Susan there is no Santa Claus.
Susan: But when he spoke Dutch to that girl...
Doris Walker: Susan, I speak French, but that doesn't make me Joan of Arc.
Little Susan pretending to be a monkey!
He may technically be one of the "bad guys" but it's hard not to feel sorry for the district attorney, especially when he starts talking like this.
Mrs. Mara: Sometimes I wish I married a butcher or a plumber.
District Attorney: My dear, if I lose this hearing, you may very well get your wish.
Kris attempting to blow a gum bubble. It's classic that we don't see this attempt, only Susan's reactions to it, and the cut to his efforts to remove the gum from his beard.
Everything involving the judge and his campaign manager.
Particularly the exchange in which the campaign manager explains to the Judge what will happen if he rules that there is no Santa Claus. He describes all the businesses and organizations that rely on Santa's image, and how all of them will vote against the Judge in the next election. He ends by telling the Judge that if he rules there is no Santa Claus, then he will only get two votes: his, and the District Attorney's. The Judge's sad response:
Judge: The District Attorney's a Republican.
Julian's plot to get his wife drunk so she'd accept Kris as a house guest and telling Doris that he'll call when his wife's "plaster - er, feeling better."