...but one of the symptoms they are missing is that those symptoms are not making it so that they can't function at work, school, in society, etc. I won't say the symptoms are having no impact - they obviously do. But they don't keep a person from functioning at all.

When I took the DSM diagnostic class in college, one of the things the professor said was that it was pretty common for students to diagnose all of their friends and family within the first week or two of class. He then went on to explain that most of the symptoms for most disorders are "normal" human behavior. They become disorders when taken to the extreme and/or when many extreme versions of the many of the behaviors are present in one individual and it keeps them from participating in society in a normal way.

That's a huge over-simplification, but you get the idea.