What was the first audience reaction to “This is Spinal Tap”? “They didn’t know what the heck was going on,” says director Rob Reiner. The film was an innovative “mockumentary.” The actors improvised every scene – there was no script. The film did OK in theaters, but became a sleeper hit on home video. It solidified the mockumentary genre and stylistically inspired some of the most popular TV shows of the last few decades, including “The Office,” “Parks and Recreation,” and “Abbott Elementary.”