You know what's funny, I never saw Desperately Seeking Susan in the theater when it came out, but I did see it on TV, but I have no memory whatsoever of the Dennis Patrick clip popping up and it's really next to impossible not to recognize him when the clip comes on screen. I wonder if the scene in which the clip shows up was cut for time? Today I caught the end of DSS on ThisTV and I don't think they edit the films they show (though they do blur nudity and silence expletives).
I just happened to catch the end of Desperately Seeking Susan this afternoon and I was shocked to see a clip from one of Dennis Patrick's grade B movies being screened by Aidan Quinn's character to an audience in a movie theater. I strongly suspect that it may have even been a clip from this film. It went by so fast that I couldn't tell with absolute certainty. But it was definitely a Sci-Fi film, which this is, and it looked like actor John Hoyt was also in the clip, and both Patrick and Hoyt appear in this film, so...