Why is Rowdy so angry in The Absolutely True Diary of a Part-Time Indian?
Junior alludes to the fact that there are demons that rage inside Rowdy. It is for this reason that he is so angry. The fact that he is a drinker at such a young age is a reflection of this anger and sense of sadness that almost cradles him. Rowdy's parents are also drinkers, indicating that there is a lack of affect and nurturing present in his life. This could also be a reason for his intense amount of anger in his being. The fact that Rowdy cannot spend time at his own house because of what is happening there and must spend much of his time at Junior's might also represent a source of anger. It is here where I think that the source of Rowdy's anger might arise.
On a more existential level, Rowdy's anger might also be the only response he can muster to a condition that lies outside his own control. Life on "the rez," the state of Native Americans, and a way of life where despair is more prevalent than redemption are all aspects of Rowdy's consciousness that effect him, and yet are impervious to anything he might do to change them. Such a contradictory state of affairs might be another reason for his anger, the one thing that can be directly controlled.