Perhaps is some universe, watching or being watched IRL while having sex is appealing—even covetable—but I think the reality is more checking your phone and locking eyes in a weird way. These two films tackle the mythic sexual interloper:
Devil’s Advocate – The dénouement of this film is that (spoiler alert!) Al Pacino’s character is both the Devil and Keanu Reeves’ character’s father. As a means of enticement toward the dark side, Pacino offers up his willing daughter to have sex with Reeves. So, basically, we have a final scene that sees our protagonist groping his sister while his father watches. Don’t do this.
Wild Things – The part of this movie you know is when Neve Campbell and Denise Richards bob around in a pool making out. What you might have forgotten about that scene is that just beyond the lifeguard stand is an icky Kevin Bacon watching and filming the two women. Give it a rest Bacon, you’ve been creeping us all out ever since Stir of Echoes.
Devil’s Advocate (top), Wild Things (bottom)