Throw Momma from the Train (1987) on Netflix

Larry Donner, a college teacher, has been having difficulties writing since his former wife, Margaret, ruined him by stealing his novel which consequently became a best-seller. He does not hide his hatred for Margaret, upsetting his girlfriend Beth Ryan, who is an anthropologist teacher in the same college. While teaching Creative Writing classes, he is stalked by a student, Owen, who wants to know his opinion about his crime tale. Larry tells him that he did not like it, and explains that in every mystery tale, the murderer should eliminate the motive and establish an alibi, otherwise he would get caught. Furthermore, Larry suggests that Owen watch Hitchcock's movies to understand the structure of a suspenseful story. Owen, who wants to kill his detestable mother, watches "Strangers on a Train" and misunderstands Larry's advice, believing that his teacher wants to swap murders to eliminate the motive. Owen travels to Hawaii and while in a ship, Margaret falls overboard vanishing in the sea and is considered dead. However, Larry does not have an alibi and becomes the prime suspect, while the deranged Owen presses him to kill his mother as part of their supposed deal.