Dom kallar oss mods (1968) - IMDb
Dom kallar oss mods: Directed by Stefan Jarl, Jan Lindqvist. With Kenneth 'Kenta' Gustafsson, Gustav 'Stoffe' Svensson, Stefan Jarl, Pundar-Bosse. The first entry in a series of films about the lives of social misfits Kenneth 'Kenta' Gustafsson and Gustav 'Stoffe' Svensson.
www.imdb.com
non-explicit, but imdb says this is first unsimulated sex scene in mainstream movies