I must agree with others who say this is not only the ultimate beach flick but also the essential 1960s teen-scene movie.
Even though the plot is nitwit (intentionally, after all), the cast is wonderfully silly. And what a cast it is: Frankie and Annette establish that this is a genuine teen-beach romp, Harvey Lembeck is a riot as the Marlon Brando wannabe who worships Marlo Branden, Don Rickles and Paul Lynde provide two different forms of wicked insult humor, Buster Keaton gives us his unique dead-pan slapstick, and we even have a pretty little wet mermaid for Bonehead (definitely Freudian).
Musical numbers, faked surfing and parachuting shots, sand, salty air -- it's a true treasure of a seemingly "innocent" time gone by even though the film was made after America lost its innocence and was getting wrapped up in what would become the Viet Nam disaster. But forget all that. Take a trip into the never-never land of the beach and get yourself a good tan, moondoggie!