During a brief recess in an honors course at Eastern Michigan University last fall, a teaching assistant approached the class’s three female professors. “I think you need to see this,” she said, tapping the icon of a furry yak on her iPhone. The app opened, and the assistant began scrolling through the feed. While the professors had been lecturing about post-apocalyptic culture, some of the 230 or so freshmen in the auditorium had been having a separate conversation about them on a social media site called Yik Yak. There were dozens of posts, most demeaning, many using crude, sexually explicit language and imagery.