Mark's manifestation of his self-awareness struggles against his own personal aversion to vulnerability. Of course, Mark doesn't mean to be a dismissive jerkface: he likes Tom alot, and doesn't want him to worry about his buddy. But, if he doesn't talk to his friend more readily, he's going to make Tom worry about him anyway.
(actually, what's really going to make Tom worry about Mark is the fact that he's talking to thin air!)
