My group has been friends and gaming together in most cases for 20+ years; a couple for pushing over 35 years. We have no written social rules. At certain rare occasions over the years (even just last year), we have had to step up and apologize for certain comments or attitudes, but otherwise we all know how each other act and react, and we have fun. I don't need to say "No Real World politics", for example. My players have seen my kids grow up, and have tempered their actions (and noise volume) as appropriate over the years.
And since I've been a forever-DM, they also know what kind of game I run (all rolls in the open, nothing fudged, yes that's a dragon on the map feel free to go visit it at level one if you want a new character). Only Campaign-specific changes need to be mentioned ("This game, you either take the Noble background, or give me a great reason why not." The campaign's name is "The Baron Wastes", and the PCs are meant to be all second- or third-heirs of frontier barons.)
When we were looking to fill an unexpected hole in the group, though (one player got a promotion, but it required a night-shift on game nights), we had trouble filling the spot. The basic social contract rule was this: You have to be comfortable inviting this person into your home. We might not be friends, but no one is accepted who you'd be embarrassed to introduce to friends and family.
Having said all that, one of my players recently (COVID) decided to try his hand at DMing. He did a great job! I played in on 5e campaign with mostly the same crew as my own D&D game, with a couple roll20-forum-invitees, though, so he did set some social ground rules ("most of us have kids, so keep foul language to a minimum"). And now I'm in a Pathfinder game he's running, mostly with people I don't know -- a larger set of social contract rules there.