When Mike (Tommy Kirk) catches sight of a new girl at the beach, he makes a beeline for her with having her his latest conquest in mind. She is Delilah (Deborah Walley), friend of Pebbles (Suzie Kaye) and holidaying with her for the summer, but immediately finds Mike conceited and resistable, having no qualms about telling him so when he goes over to chat her up. Suitably chastened, he is nevertheless not going to give up so easily, and eavesdrops on Delilah and Suzie as they discuss him. Then he comes up with a plan: he will pose as his own brother, donning spectacles to look like a real square...
It's a Bikini World was one of the final entries into the beach movies cycle of the sixties, and even A.I.P. were turning away from them by this time. For that reason, for its end of an era tone as the innocence of that type of film began to alter into something more self aware and even jaded, this holds some interest, especially as it unintentionally has an oddly forlorn mood to its silliness. That could be because of its stars, Kirk and Walley, who had made their name in innocuous fare, and were seeing their opportunities begin to slip away as their fans were moving on: 1967 was the Summer of Love, after all, not something alluded to here.
Kirk in particular was struggling to find appropriate movies to appear in, mainly thanks to having been dropped as a Disney star thanks to his homosexual lifestyle, and that scuppered the rest of his career. Here he comes across as happier in the nerdy Herbert role than in the obnoxious jock role of Mike, probably because the former offered him more opportunities for comedy, but it's really Walley who came off best here thanks to the scripting and direction by one of the few female directors of exploitation movies around - even today, Stephanie Rothman is notable for her gender perhaps more than her artistic achievements.
This meant that It's a Bikini World had more of a proto-feminist theme to it than anything Frankie Avalon ever had to contend with from Annette Funicello, although much of the dynamic between Mike and Delilah is the same. It's just that while she prefers the quiet, sensitive, bookish Herbert persona, she is actively aggressive in her reactions to his counterpart, and insists on trying to beat him in various physical competitions organised by local entrepreneur Daddy (Sid Haig with hair!). Moves towards the changing times abounded, as for example there's not one scene where anyone gets onto a surfboard - nope, here the cast take to skateboards instead, although modern viewers will find their skills unspectacular.
For many, the most interesting aspect will be the music, as ever with these movies there are bands ushered on to break up the comedy, such as it is. The famous one is Britain's own The Animals, looking as if they really mean the sentiments of their number as they perform We Gotta Get Out Of This Place, but the passing fads are plain to see by the length of the band members' hair compared to the conservative haircuts of the actors. Also showing up were two one hit wonders, The Toys not doing A Lover's Concerto, and The Castaways doing their cult classic Liar Liar, a storming record which perks things up a lot. However, they missed a trick because lurking in the cast as Mike's best friend was Bobby Pickett, aka Bobby "Boris" Pickett of Monster Mash fame, and he doesn't get to sing one of his novelty songs. For nostalgists, this is a far more promising prospect for entertainment than anyone else, but that casual melancholy informs the proceedings, not something that would have struck many at the time.