It’s a concept from the time of Locke and Hume where the idea was that by being in proximity to humans in the same locality that you consented to the laws and traditions of that locality which those humans supported. It’s a messed up notion, but I might be wrong on its exact formulation.
There is one social contract and only one: don’t hurt people and don’t take their stuff. If a person isn’t willing to abide by that rule, then he has no place in society.
EVERYBODY knows this; which is why everyone tries to hide their aggression against a fellow man.