Bob and the circle salesman
Who remembers an old sketch with the Shape Salesman from Saskatchewan?
In a plain behind-the-wall segment, an Anything Muppet was a representative from a shape company who tried to sell Bob a circle. (Note that this was NOT Lefty the Salesman; this guy was a lot more boisterous and outgoing.) However, Bob made it clear from the beginning that he wasn't interested in any circles. Nonetheless, this persistent circle salesman kept showing different sample models to Bob, each in different sizes and with differing patterns. One was a compact circle that you can "carry... in pocket or purse". Still, Bob kept on refusing to purchase.
Then the salesman dug deeper into his stock. He pulled out a "4-sided circle". Now not only was Bob fighting off a high-pressure sale, he had to explain that he had a square, not a circle! The salesman didn't wanna hear it; he was a "Circle Salesman" and knows his circles. So then he brought out a "3-sided circle" which he actually gave to Bob free of charge. Bob was yelling "Mr <whats-his-name>, this is not a circle!" while waving the shape as the salesman walked away. Alone, Bob quietly and frustratingly said something like "This guy doesn't know the difference between a circle..., a square..., and a triangle."