The Outtakes During the End Credits
Outtakes during the end credits are now rather a movie cliché(perhaps less used in recent years, come to think of it), and should only be used for "minor" movies -- most usually comedies. Who would want to see outtakes from The Exorcist or Psycho or Silence of the Lambs of the actors blowing their lines and laughing; it would rather end their status as classics.
But lightweight comedies? Sure, why not? Heck, with a lot of these comedies the outtakes are funnier than the scripted humor within.
So it is with the outtakes of "Grumpy Old Men."
This makes them funny throughout: we hear accordion-styled Polka music throughout. And Polka music is two things: upbeat and funny.
Then there is the stylistic device of continually cutting back to the same scene -- Old man Lemmon and his Older Man dad Burgess Meredith, spying out a window at Ann Margret taking Ossie Davis into her house -- with a new line for Meredith each time:
Looks like he's taking the log to the beaver.
Looks like she's gonna ride the baloney pony.
Looks like he's takin' the skin boat to tuna town.
With Lemmon yelling "DAD! Would ya stop that!" every time.
(None of those lines made it into the movie; I cannot remember which version did.)
Also this: it becomes clear in the outtakes that while Lemmon pretty much remembered his lines fine...Matthau did not. Matthau had had heart surgeries and other problems, it may have affected his ability to memorize. Nonetheless, Matthau made the most of his blown lines, and Lemmon laughed along.
So you've got Matthau going "Did I....?(Loses line) Would I? Should I? Could I...?"
Or Matthau forgetting his line as Ann Margret opens her door to let him in and he switches to "Hello, I'm Ronald Reagan. I used to be President...I was a lousy actor, though." A-M is funny, realizing Matthau has blown the scene and playing along with him: "Certainly, welcome, come right in."
And I like a staged shot of Matthau watching Lemmon's car driving into the distance...and suddenly Lemmon appears beside him, saying "Who's that?" Matthau turns and very legitimately laughs. Its the "real deal," between two real friends.
But Burgess Meredith steals the show.