Mark's lapse into the third person - "He's ... on the outside, looking in" - helped me realize what had disturbed me about him from the start.

He seemed fake, as if playing a role.
...
Everything about him, down to his carefully chosen, probably pricey, "worn out" clothing felt scripted.

It is a kind of identity disorder I believe has its roots in a society that has drifted free from reality and is creating adolescents (and, I would venture, people of many ages) who are at most participant-observers in their own lives, with little genuine emotion - like actors playing themselves.