o.b. – bastun - The sauna (1978) - (Sweden)

As a couple of young women are playfighting in the public shower of an obvious sports place, our heroine walks off while trying to dry her hair. She wanders through halls as the VO explains: 

"For girls who want to be able to move freely, even though they have their period, we make a tampon called ob. It doesn't allow itself to be disturbed by any sports, whether above or below the surface of the water."

Well, that sounds very good, as if you might even forget you're wearing it, or where you are going, and the young lady walks into the men's sauna area by mistake. 

Tagline: "Don't make a situation worse than it already is."