There was a lot of confusion when This Is Spinal Tap hit theaters in March of 1984. Audiences weren't that familiar with the concept of a mockumentary, and some viewers even left the theater thinking it was a real documentary about an actual band. When you think about it, "Big Bottom" and "Tonight I'm Gonna Rock You Tonight" weren't that much crazier than some of the metal songs of the time. Making matters even more confusing, Spinal Tap did (sort of) become a real band; they have three legit albums and many other fictional ones. The whole thing poses all sorts of existential questions. All that said, This Is Spinal Tap is a monumental movie that wasn't fully appreciated at the time. If anything, it's only gotten funnier with age.