The Birds (1963)
I was surprised that this movie inspired the complaints it did from my movie-watching partner, and now I have the beginnings of an explanation. Hold on to your butts.

The scary movie relies, for its impact, on two moments: (1). the bump of 'the thing that goes bump in the night' that will (ideally) get your heart a-racin' and (2). the Wizard of Oz moment in which the curtain is pulled back from some mysterious monstrosity and you get some kind of explanation of why/how it is going about inspiring terror. The first is unsettling, while the second is comforting. These moments are, for this reason, usually linked or at the very least, balanced. The Birds, in contrast to most movies of its type, foregoes the second altogether. To unmask the birds, to explain what made them tick (or attack in this case), would dilute their power to frighten, which is why, I think, their attacks occur without any discernable reason. That's what sets The Birds apart from every other scary movie about ants, spiders, werewolves, manatees, and anacondas (They got snakes out there this big?!). The bird attacks are, at rock bottom, irrational and inexplicable.

In the face of this lack of reason, however, my parner in crime expressed disappointment that the personalities of the various characters and their relationships to each other seemed "random." A more traditional horror movie would have featured a rogue ornithologist/bounty hunter, the president of PETA, the ex-husband of the PETA president (whose mother was devoured by sparrows), a down-on-his-luck biologist who has a pet canary, and a billionaire heiress who dated the ornithologist and whose fortune was made by selling radioactive bird feed in the Amazon, all of whom are thrown together by fate when their plane crashes in the middle of Brazil, conveniently close to the nest of a large (radioactive? mutant?) condor (bluejay? hummingbird?). The plot would probably have been lifted wholesale from a Choose-Your-Own-Adventure book. But a traditional horror movie is, I think, what The Birds is not.

It was, I now believe, the lack of these traditional links between the characters and their horror-movie situation that threw my compatriot off. On the other hand, perhaps he was just underwhelmed by the acting.