This is something that people understand very easily when it comes to interacting with other humans – we don’t sit on the laps of strangers, we don’t hang all over strangers, and most of us don’t excessively hug or kiss strangers.
In fact, getting into another human’s space is such an awkward action, we came up with a standardized way of getting into each other’s space so it doesn’t come off as hostile or awkward – the disarming handshake in our culture (in Europe and other cultures they have a similar, but still easily understood social protocol for entering a person’s space).
However, this basic concept that is so intuitive in our day to day lives with other humans is oddly difficult to apply to our dogs.