I am aloof by nature. I mind my own business. I'm good with everyone, and I get along fine with people. But work is work, and friendship is friendship. I never mix the two.

This quote means that the person is friendly and polite with others, but they keep their work and their friendships separate. They do not interact with their friends at work, or bring their work into their friendships. They make sure to keep these two aspects of their life separate and distinct.