I'm a 67-year-old woman who saw this while visiting Dallas back in 1972 and never forgot it. The ending totally caught me by surprise because it was so unexpected -- and because back in those days words like "ass" were not standard fare in cartoons. I even told people about it in the following years because I thought it was so funny.
Today I decided to google the title and was thrilled to be able to see this again.
(And I do miss cartoons before main features!)