Fasten your snorkels. It's gonna be a bumpy dive.

National Lampoon's Last Resort

Sam and Dave are living the boring life until they are beckoned to Sam's uncle's Island. When they get there (still not quite sure how that worked) they are compelled by beautiful women and a dastardly enemy of the Island. After accidentally convincing Sam's uncle to sign away rights to his island, they must somehow fix the problem.