One wouldn't know it from watching the pathetic Disneyfied versions, but the original Muppet Show of 1976 was in its prime one of the slickest and smartest series ever seen on television. The writing was wonderful, the characters unique and appealing, and their execution was flawlessly funny. Every so often they would use a running gag that ran for the length of the show (early in its history, the Pigs once took over the show as a prime example of such) and that is what we have here.
When Mac Davis was the guest star in a late 1980 episode, a running gag involving Beaker, the hapless laboratory assistant performed and voiced by Richard Hunt, ran throughout the episode, culminating in a very unique ending. Below are linked the segments of this show that comprise the running gag in full, followed by its IMDb data. So grab the kids and watch wholesome comedy at its peak; you won't find it many places today.