The social distance corollary is a fancy way of saying that people tend to behave differently toward each other based on how close or far apart they are in terms of their social status or category.
Let's say you're playing on the playground with some of your friends. You might go over and give your best friend a big hug because you feel close to them and they're in the same social category as you. But if a teacher comes over, you might not feel as comfortable giving them a hug because they're in a different social category than you are.
The same thing happens in other parts of life, too. For example, if you see a celebrity on the street, you might feel like they're in a different social category than you and treat them with more respect or awe than you would someone else.
This social distance corollary can also impact how we interact with people from different cultures, races, or ethnicities. If we perceive someone as being different from us in a significant way, we might treat them differently than someone who we perceive to be more similar.
While it's important to recognize and be aware of how our own biases and social categories impact how we treat others, it's also important to try to treat everyone with respect and kindness, regardless of their social status or category.