I've heard that a lot of companies are having issues with off the clock social media. Some states have had to pass laws that keep employers from demanding social media logins so they can monitor if what an employee does on their downtime are activities unfit for the image the company wants to portray. One teacher lost her job because she posted a picture of herself at a party dressed as a pirate holding a drink. Employers crawl through known social media to look for posts made during sick days, looking for reason to discipline for lying about calling out. Some people have been denied jobs because of pictures a few years old, not days old, and that includes young 20 somethings that were understandably stupid minors when the pictures were made.
It's all about protecting the image of the company from anything that any employee does at any point of the day, whether on or off clock. An underwear pic off the clock doesn't seem like a big deal, until you get some ultra conservative running across the photo and screaming to like minded news media about how [insert name here] Company employs people posting obscene smut that is borderline pornographic where children can see it. That is a PR nightmare, double nightmare if other news agencies run with the conservative media's story, and companies will want to get rid of the employee in order to say "We did not know and we do not tolerate pornography or indecent liberties of minors" even though it was nothing of that, just an everything covered photo meant to stay between friends.
However, it's wrong to say that people must not have a legal social life when the company isn't paying them to behave a certain way. They want to do that, they need to pay 24/7. And there's not a single person in this world that doesn't have plenty of moments in their life where they were immoral, downright illegal, or just plain crazy as shit in their conduct and they are just lucky no one had a camera.