Throughout the story, Finny demonstrates his adverse relationship with authority in general. While he tends to abide by the given rules in most "official" situations, when he is on his own or spending recreational time, his attitude and actions reflect his dislike of boundaries and structure.
Remember, Phineas is the one who instigates most of the hazardous adventures that he and the narrator enjoy. While Finny's life tends to be one without borders or confinement, he speaks of authority with a healthy degree of respect, at the same time.
" Phineas didn't really dislike West Point, in particular, or authoriy in general, but just considered authority the necessary evil against which happiness was achieved by reaction, the backboard which returned all the insults he threw at it." Phineas sort of thumbed his nose at authority. He knew there were rules that had to be followed, but he also enjoyed walking on the edge between what was supposed to be done, and what he wanted to do.