10. Rex Reed - Superman
The Christopher Reeve-starring Superman '78 features an extremely bizarre - and easily missed - cameo from infamous film critic Rex Reed.
Donner convinced Reed to make a brief cameo in the film as himself, entering the Daily Planet offices just as Clark (Reeve) and Lois Lane (Margot Kidder) are leaving. Hilariously, just as Clark starts to introduce himself to Reed, the critic completely ghosts him.
Though Lois does indeed refer to Reed by his first name, you'd need a keen ear and precise knowledge of what Reed looked like over 40 years ago to even have a chance of catching this.
Somewhat amusingly, Reed went on to pan Man of Steel by comparing it to Donner's film, calling it "an overproduced $225 million comic book with delusions of grandeur that was better made in 1978 and a lot more fun."