The end of the episode with Sammy Davis Jr: He kisses Archie on the cheek, cueing a Heroic BSOD. The studio audience laughed for so long, actually setting a record, that the laughing had to be shortened for the broadcast version.
In one episode, Archie finds himself locked in the basement. With nothing else to do, he drinks himself stupid and when a fireman comes to bust him out at the very end, he's so wasted, he thinks it's God coming to take him to Heaven. Then the fireman in question turns out to be...black. When Archie lays eyes on him, he immediately drops to his knees and cries, "Forgive me, Lord!" as the audience roars. In an odd way, this also doubles as a Crowning Moment of Heartwarming.
Even funnier is his followup comment, which closes the episode: "The Jeffersons was right!"
"Edith's 50th Birthday" is rightly listed on the pages for Nightmare Fuel and Tearjerker, but there is one moment, at the beginning of the second episode of the two-parter, that does a lot to lighten the tension. Edith is shakily explaining what happened to Archie, who realizes that her attempted rapist must have been hiding in the house when he briefly came over to get a punch bowl. Edith explains that the rapist forced her to remain quiet, or he "would have done something to you." She means kill him (he had a gun), but Archie takes this in a totally different and hilarious way: "Done something to me? What was he, a fruit, too?"