It actually was quite funny. They set it up that it was meal time, and Becky was long-since due home and late. And when she finally arrived (and Goranson made her re-entrance to the show), the character of Roseanne snapped at her, "Where have you been??! We've been waiting for you." And yes, it got a huge laugh from the audience.
But that wasn't the "especially funny and clever thing they did." That came during the closing credits. If you never saw it, it's really smart and a total hoot. The did a parody -- even duplicating the black-and-white -- of the opening credits of the old Patty Duke Show, where Duke played look-alike cousins. ("They're cousins, identical cousins all the way. They laugh alike, they walk alike / At times they even talk alike...") Only here, they wrote news words -- that are pretty funny -- about "Nearly identical Beckys." There's also a very funny homage near the end that I don't want to give away. But you have to know the Patty Duke Show to get it. I don't want to give anything away of what to look for, but I'll explain it at the bottom, after the video. (Also, since some of the words fly by and are hard to understand, I'll post the lyrics below, as well.)
And indeed, here's the video of that parody. Also, for those who don't know The Patty Duke Show, the person who made the video edited in first the original opening of that show, so you can see and hear what's being parodied.
Okay, here's what the homage joke is.
I'll skip a few lines, so your eyes don't accidentally drift to it.
Here it is -- at 1:55, you see John Goodman, who played the father on Roseanne, along with another older man. That is longtime character actor William Schallert -- who played Patty Duke's father on the The Patty Duke Show!
Interestingly, Schallert himself was involved in a character replacement. When the actor Ross Martin was playing the sidekick Artemus Gordon on the series The Wild, Wild West, but he sadly passed away. William Schallert was hired to replace him, albeit with a different character.
And here are the lyrics --
Meet Lecy the one you used to see, from '88 to '93
Then Sarah came and took her place
Because she had a similar face --
Just like on TV.
They're Beckys, nearly identical Beckys all the way
One pair of matching actors but only one part to play
Sarah loved that dopey Mark and wound up in a trailer park
Our Lecy showed some Lecy skills
She wants a house that's not on wheels
What a crazy pair.
They're Beckys, nearly identical Beckys and you'll find
They walk alike, they talk alike,
Abruptly leave the show alike
You could lose your mind
When Beckys ain't two of a kind.