dumbest reason to do a PhD

Would you enrolled in a PhD program just out of spite?

Background: X is a Masters student under the guidance of Prof Y. Prof Y stopped X from getting his Masters by giving X a failed grade for his Masters thesis while all other members in the thesis panel gave him high marks. In the end, X had to find a new advisor last minute, but managed to graduate. X is a well-established professional in his own field and is rich. The Masters degree was just another feather in his cap.

Now: X has enrolled in the PhD program within the same department as an attempt to 'spite' Prof Y and has chosen another prof, Prof Z, as his PhD advisor. Also, X 'purposely' took Prof Y's classes so that he can rub 'it' in Prof Y's face.

When I first heard about this, my first reaction is "what a stupid thing to do!" and "what's the point?" In my opinion, to do something just to spite someone is the dumbest and most childish thing to do. If he likes to do research or he wants to get a foothold in the academia, then by all means, go get a PhD. But to do a PhD just so he can 'rub it' in his ex-advisor's face is probably the most moronic act of self-sabotage.

What can X hope to gain from such shortsighted action? Prof Y is an experienced researcher and noted scholar in his field. Although he is quite controversial and sort of a loner, he is still a senior faculty member of the dept. Will Prof Y even care that X is back as a PhD student? Or care that X went to Prof Z instead of him for guidance? If X does well in his PhD, Prof Y can still claim credit to X's success since he did guide X for almost 2 years. If X doesn't do well, Prof Y can declare that he had foreseen what a failure X is and that's why he failed X's Masters thesis. It's a NO-WIN situation for X.

Everyone who knew about this backstory was egging X on and is sharing this story around like some juicy gossip. Frankly I just don't get it. Maybe some people just need some excitement in their lives. Me? I think I'll skip.