We don't know what it is about watching people scaring other people that is so satisfying. Maybe it's the relief that it's them and not us.
This college student that scared easy lived with the possibility of terror at every turn while living with housemates, who reveled in scaring the bejaysis out of him at any opportunity (and recording it for posterity). Not even the bathroom was safe, which is unfathomably cruel. We've all seen Psycho.
And yet, we still laughed.