This is because he gets talked into taking a ballroom dance class that he really doesn't want to attend. Elly is all for it and doesn't understand his standoffish reluctance and feelings of self-consciousness until she bears witness to his having a flashback to when some girl he liked dumped him for a dude with a guitar or a better car or something; he then goes on explain that when he was in high school, he felt like an outsider no one really liked. It's strips like that which go a long way towards making my arch comment about how John and Elly's real reason for marrying when they did is that each is the first person two lonely outcasts dated more than once.
Of course, where sympathy turns to mild contempt is that John never seemed to, well, you know, try to share his experiences with his son in order to, shall we say, get to know the real Michael instead of the super-crazy, no way media monster Mike he needed to believe in because otherwise, he'd actually be a panicky nitwit leaning on a sitting duck because he's stupid enough to believe in monsters. Simply put, John's dimwitted need to believe in whatever mush unworthy authority figures told him to believe and servile obedience to their command to ignore the evidence of his own senses got in the way of his ever realizing that Mike was an okay kid with the same problems he had.