Let's not call it a "social contract," let's just call it etiquette so everyone has fun.
If you sum everything up to this top rule, we'll likely get along fine. We're getting together to play a game together and enjoy one another's company. This shouldn't be hard.
If you have to get a lot of clarification on what is involved in being a dick, or want to split hairs on what might be dickish, you just might want to look within on this one because I suspect you truly have the answers to this if you dig deeply enough. Coming at this in bad faith is a dick move, after all.
We're all adults so I don't feel like I should have to say this, but I'm going to put it out there regardless:
We're all here to have fun, but not at the expense of one another.
Again, this should be a given but I've been surprised at times that it's not. It's about respect:
So do most of the gamer stereotypes, but rules laywers are by far the worst. Just… don't. (He who lives by the sword dies by it. Repeatedly.)
Only in-game politics and religion at the table, none from outside. We didn't come here for that.
If you need to take a call or text a lot, please step away from the table. It's distracting to other players and if it becomes a problem you'll be asked to leave the table and/or game.
If you can't hang with old-school gaming then there will be problems. For instance, if you can't handle that character fatalities can happen then this isn't the game for you.
We're all here to have fun and play a game. For some, it's not fun to have someone else in the party who is edgy or brooding just to be edgy or brooding, or going around stealing from party members, attacking them or causing trouble because "they're doing what their character would do." (I'll admit, it's not fun for all DMs, either.)
I know you're supposed to roleplay, but having to watch your back against the world and also your compatriots or suffer the consequences of someone who is random for no purpose but their own edification is just… exhausting. It's also not fun. At the table, let's agree that the party are all allies and we hunt the monsters, not be the monsters.
When a new player joins a gaming group it's a bit like dating: sometimes the fit is right, sometimes it's not. Even though this is intended to be an open table game, we all still need to get along. If you are not enjoying the game style, old-school rules or just another player, let's talk about it. I suspect we can come to some resolution or understanding that is acceptable.
However, the reality is that if we can't work it out maybe this just isn't the game or group for you. Trust me, no gaming is better than bad gaming, and life is too short to do something you don't enjoy. I want to game to have fun, and I want everyone at my table to have fun!