We discussed this "lost" clip a few years ago, but I happened to think of it again recently.
Backstory: The stock image site alamy.com has an image that depicts Tina Sinatra and Robert Wagner (who at the time were engaged in a brief marriage) after some pie throwing action.
Alamy wrongly pegs this and other images from the same group as possibly being from Wagner's late 60's drama series "It Takes a Thief." However, although Sinatra guested on that show a couple of times, this is not from any scene in those episodes.
Looking at this image and others from the group, it appears to be from some TV special or variety show. Thing is, I have searched through IMDB and scoured other web sources, and I cannot find any such program from the era (1967-1970 or so) in which both Sinatra and Wagner appeared.
There aren't many left in UMD Land who have any interest in finding "lost" mainstream clips, but I thought I'd mention this one again in case anyone feels like playing detective on this.