The first character to utter an "F-word" in Stranger Things was Dustin Henderson, in the episode "The Monster" of season 1. This occurs during a scene where Dustin is talking to his friends about the Demogorgon.
While the exact word used is not audible due to the show's editing, it's clear from context and the characters' reactions that it is a vulgar term. This moment is significant as it marks the first time the show uses profanity, signaling a shift towards a more mature tone as the series progresses.
