Bless the Beasts & Children (1971)

Boys in a summer camp cabin are seen in bed at night under the covers with up and down movements, implying they are masturbating, while a voiceover warns against resisting temptation.

While there is no nudity, there are multiple scenes with teenage boys standing around in (sometimes wet) underwear which leaves little to the imagination.

A large group of boys haze a smaller group of boys with paddling. They then throw a pot of urine on the boys.