Maneater

It doesn't get much more unrealistic than this movie. There were absolutely no attempts made to make the shark and shark attacks look real, and one of the main characters blatantly flirts with a taken man right in front of his significant other. This is essentially a cheesy slasher film with a shark replacing a human serial killer. At one point, just like in your typical horror movie, two people go off alone for obviously scandalous reasons and somehow their friends don't notice they're missing right away. And of course one of these people were explicitly told not to go in the water, but of course they do.