I think that the title is appropriate for a couple of reasons. The first is that it represents the gulf between father and son. One can almost imagine Parvez saying this to his taxi cab colleagues with a sense of despair and lament not because of his son's condition but because of what it will reflect on him as a father. One of Parvez's fundamental challenges, and failures, as a father is that he is so committed to what others think of he and his name that he believes, wrongly, that his son will follow the same philosophy. This marriage to the West is something that actually serves to drive a wedge between he and his son.
Another reason why the title is significant because it is meant to be ironic. In the end, the father is more of a fanatic than the son. The father is the one who abuses a child who is praying and splits his lip open in a drunken rage. He is unable to communicate anything other than anger and wrath because of what his son has become: A devout Muslim. It is here where the title is most appropriate because the "fanatic" is not the son, but the father. However, society, as biased as it can be against things it does not understand, would most likely see the son as the fanatic and not the father, for it, too, does not understand why its values would be rejected. In this, further alienation of the youth is present, leading to greater labels of fanaticism for that which is not understood, making the title not only appropriate but quite prophetic and ominous.
I also share the opinion that the title is fitting, because I would call a person with the same attitudes und beliefs towards the islam like the one's ali has a fanatic person as well.
Ali speaks of "our" people although he is an english citizen who has never been in the near east and says that western materialists would hate "them".
Furthermore he follows stricktly the Islamic rules of which he even had made fun of some time before and adjudges even his own father as awful because of not following them.
All this are aspects which make people accusing someone of a fanatic way of thinking and because this is indeed the main conflict in this short story I would call "My son the fanatic" a fitting title.
I also think that the title "My son the fanatic" is fitting, because Ali acts as if there was nothing more important in his life than his religion. When you're interested in a culture or a religion, it's normal that you accommodate your behaviour a little to it, but Ali really exaggerates and goes too far by, for example, hurting his father or Bettina. So, in general, the title is fitting.
I believe it is fitting, but I also believe it is extremely cliché.
I think the title "My son the fanatic" is fitting, because Ali´s behavior is getting more and more radical. He is blustering into the Islamic faith and culture so much that he is no more caring about anyone else, neither about his friends, nor about his family. Because of this he can be called a "fanatic".