This marvel was filmed in 1966. At that time, it's quite astonishing to realize, the period between the high point of the Andrews Sisters' career and that of the Supremes right about this appearance was something like half what it is between then and now. Then, the simple thought of one doing the other's material was inherently hilarious - that was what made it camp, then. Patty, Maxene, and Laverne are clearly coming off of some sort of Flapper Number and so must have seemed especially antediluvian next to the Ultra-Now Supremes, making the contrast all the more potentially ludicrous.
From our perspective now, though, it's clear that both do just great with what they're given, and if anything the Supremes' column dresses, wigs, and carefully ladylike demeanor seems just as period as the Andrews' boas and pearls. Therein, in fact, lies the camp from today's angle: the distance that both groups have from us, and the unexpected success they wring from the setup. Not to mention the presence of Sammy Davis, Jr., always an en-camping, as it were, presence in almost any setting.
And, to top it all off, we get a truly classic Diane moment at 1:28. Why no one has ever hauled off and just slapped that woman I will never know.
As always, this one's for St. Flo, here for once right in the middle.