The Blue Lagoon (1980)
The tale of two cousins stranded on a tropical island as children and left to slowly develop their sexuality together in an uninformed vacuum, Blue Lagoon is meant to be a deep dive into the raw and innocent core of human eroticism. The execution, though, is a long, awkward, and poorly assembled hack-and-slash attempt, made somewhat creepy by the fact that its female lead, Brooke Shields, was 14 when they shot the film. But it ultimately deserves a spot on this list for being perhaps the preeminent film trying to sell us on having sex in nature — on leaves and beaches. But as anyone tempted by a sex-on-the-beech movie can attest, things pretty quickly get sandy, bumpy, and ultimately grating and unpleasant.