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.
Even his reaction is funny, where he's surprisingly unflappable about it. "What the hell, he said it was in his contract".
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?"
Archie and Mike had arguements with Edith and Gloria respectively and are forced to share a bed. Mike gets a glass of water and accidentally spills it in the bed. Archie doesn't think it's water....
Archie: (wearily exasperated) You got into this bed with me....to do this here....
Mike: It was an accident!
Archie: With little Joey, it's an accident. With you it's a dishonorable discharge.
During the final season, Archie, Edith, and Stephanie visit Mike, Gloria, and Joey out in California for Christmas. When Archie asks little Joey if he remembers his grandfather, Joey smiles at Archie and gives a quick raspberry, to Archie's utter delight.
One early episode had Mike claim that Archie belches exactly 10 seconds after drinking Alka-Seltzer, to the point that you can set a watch to it. Later on, Archie drinks a glass during a conversation with Mike; while Archie prattles on, Mike starts quietly counting down from 10, and as soon as he reaches 1, Archie lets out a good sized belch.
The very first time we hear the toilet flush on the show...prior to this, it had NEVER been done on tv. The audience reaction says it all.