Sorry, I'm real vague on this one guys ... but it might be a teen type movie from the late 1970's or 1980's. All I remember is the ending. It ends with a crowded beach with all these hot girls going into the water and a couple of young guys grinnng ear to ear. As soon as the girls' bathing suits hit the water, the fabric will start to dissolve leaving them all naked! The guys know this is going to happen, but no one else does! Sorry, I can't give you more info.