Crazed Fruit (1956), directed by Kô Nakahira.
In Japan, after the Occupation, a gang of rude rich kids spend their summer on the shore, drinking, water skiing, being bums. Two brothers meet a girl with secrets. Cupid gives it to them all, good and hard. Tragedy.
Remarkable effort from a first time director. The DVD commentary track has quite a lot on how the film was a breakthrough in Japan, and how influential it was.
Criterion DVD.