The Unhoneymooners (1970)

Olive Torres and her nemesis Ethan Thomas, are the only people not affected when Olive’s sister’s entire wedding party gets food poisoning. Suddenly there’s a free honeymoon up for grabs, and Olive will be damned if Ethan gets to enjoy paradise solo. Agreeing to a temporary truce, the pair head for Maui to assume the role of loving newlyweds. Novel adaption of the same name by Christina Lauren.