Les diaboliques (Henri-Georges Clouzot, 1955).
I had a friend around a decade ago whose girlfriend was horrified whenever she would catch him having opened his eyes to glance down at their interlocking parts during sex. “Stop looking,” she would say. He was fool enough to tell us this and naturally we all started to say it to him all the time, and it caught on well enough that it became a thing to say it even when he was not around. “Stop looking!” we’d tell each other.
They’re married now so I assume either he stopped looking or she let it go.