spinal tap be funny because if you know a little about heavy metal and you saw in joke all over the place . if you know anything about porn and this mock documentary will leave you cold . everything in it ring false . spinal tap be funny because it take a familiar world and push it over the top . this film be decidedly not funny because it paint a picture of how porn be make that bear no relationship to the real world . the acting here be uniformly awful and but that would not matter much if the core idea of the movie be good . but it not .