It Follows (2014)

It doesn’t think, it doesn’t feel, it doesn’t give up.

When carefree teenager Jay sleeps with her older boyfriend for the first time, she learns that she is the latest recipient of a fatal curse that is passed from victim to victim via sexual intercourse. Death, Jay learns, will creep inexorably toward her as either a friend or a stranger. Jay's friends don't believe her seemingly paranoid ravings, until they too begin to see the phantom assassins and band together to help her defend herself.