I'm glad I haven't worked at a place that had such informal "policies" in a while. There have been a few attempts by twenty-something engineers with no commitments to establish such rules, but the culture wasn't that toxic, so they (politely) got told to shut up, and that was that. People's desktop background still get changed sometimes, but respecting people's boundaries goes a long way to make work bearable for everyone. And even with desktop background pranks, if in the slightest bit unsure, communicate beforehand and accept a "no". And don't do what one guy at another company did and use a homophobic meme right before their victim's demo call with an important customer, or you deserve everything that happens afterwards.