When I was a kid in the 80’s I briefly saw part of a movie in which a high school boy and possibly a girlfriend, go in to their mean high school teachers house. The teacher somehow gets beheaded and the movie ends with the kid in class and the teacher walking down the aisle seemingly fine, but wearing a scarf, and he takes the scarf off while using one of those large paper cutters. It’s haunted me for years. Any ideas? I know I did not watch the whole movie.