The final episode. Parricularly the two Darryls telling their wives to shut up.
The episode where Dick and Michael hold an audition for Dick's "sexy, young co-hostess". The first auditionee is a giggly, irritating ditz. The second is a Straw Feminist that causes both Dick and Michael to shudder. The third is an attractive, intelligent college graduate. At the end of her audition, Michael asks Dick what he thinks. "No contest." "Couldn't agree more." Dick shows up for the first day of shooting only to discover that Michael chose the ditz.
During the plot-arc when Michael is having severe financial trouble, and he returns from a very unsuccessful trip to the local hardware store:
Michael: I've never seen a credit card cut in half with an axe before!
Stephanie: (Involuntary squeak of horror)
That same episode had this hilarious dialogue as George "comforts" Michael:
George: Michael, I know how difficult this is for you and I know what you must be going through.
Michael: Really? You mean you've been unemployed too?
George: Nope, been working at the Stratford since I was sixteen. Been here ever since. It's a good feeling.
Joanna: (realizing that George isn't really making Michael feel any better) Uh, George, don't you have some work to do?
In "Take Me To Your Loudon", Dick is trying to do damage control during a costume party. Long story short, in complete darkness, we see only six flashlights being flashed around. The next thing we hear? "Hi, I'm Larry...", followed by pandemonium from the studio audience.
In "The Boy Who Cried Goat", when Dick tries to tell Kirk the story of "The Boy Who Cried Wolf", only to be interrupted by the others who had all heard the story differently.
At the very end of every episode, there was the Vanity Plate showing the MTM kitten meowing. Only instead of actually meowing, what one heard was the kitten meowing in Bob Newhart's deadpan voice.
In the final episode, one heard the kitten yelling, "QUIET!" in the two Darryls' voice (see above).