Late to the party, but I remember watching the original show that had the “Sis Boom Bah” line. I was a kid (I used to love staying up to watch Johnny Carson - made me feel very “grown up”) and I thought it was the funniest thing I’d ever heard. I’d never seen a joke that just completely destroyed the audience and the comedians like that, and I laughed myself silly over it. Never once did I even consider anything about cruelty to some hypothetical sheep. It was just funny as hell.
The only other joke I’ve ever seen that affected everyone involved the same way was Richard Simmons on “Whose Line Is It Anyway?” If you’ve seen it, you know the one I mean. I laughed my ass off at that one, too.