Let’s separate this into two questions:
- What was the first commercial, non-porno motion picture to show a man’s penis (excluding ethnographic films)?
Dante’s Inferno (Italy, 1912), in a far shot, showed nude males being led onto a boat on the river Styx.
Kameradschaft (Germany-France, 1931), in far shots, showed mine workers showering in the nude.
I Am Curious (Yellow)(Sweden, 1967), lead actor Vilgot Sjoman see nude several times, including closeups of his genitals. An international sensation. Released in the U.S. in 1969.
If… (UK, 1968). Revolt at a boy’s school. Two versions were filmed of a scene in which rule-breakers are forced to stand in cold showers. In the more explicit of the two, frontal nudity from actors Macolm McDowell, Guy Ross, and Richard Warwick.
Women in Love (UK, 1969). In this adaptation of D.H. Lawrence’s novel, famous nude wrestling scene with actors Alan Bates and Oliver Reed.
- What was the first commercial, non-porno Hollywood motion picture to show a man’s penis (excluding ethnographic films)?
Mom and Dad (1945). This independently made exploitation feature directed by Hollywood mainstay William Beaudine, about a teenage couple who get into “trouble”, includes documentary footage of a VD-ravaged penis.
Medium Cool (Paramount, 1969). Robert Forster has sexual romp through house with girlfriend, with casual frontal exposure.
Drive, He Said (Columbia, 1971). College rebel, played by Michael Margotta, runs across campus, then frees animals in biology lab, all while naked. Lengthy frontal nudity, directed by Jack Nicholson.