Provide the theme summaries for the following conversation: 

John: I am so angry, Al.
Al: ???
John: My supervisor postponed the meeting again.
Al: Gosh, he's really crap.
John: I know, I'm thinking about changing him.
Al: Do it.
John:  You know it's not that easy.
Al: Why not?
John: The whole procedure is complicated and I would have to give a reason.
Al: Like "he is crap"?
John: You cannot say it openly at the department
Al: That could actually create only more problems.
John: Exactly.
Al: it would be good if he resined himself.
John: But should I suggest it to him?
Al: Maybe you could. 
John: He actually seems a nice person, he's just a horrible supervisor.
Al: yeah, a nightmare of every student.
John: I will try to talk to him next time.
Al: Good luck with it!
John: Keep your fingers crossed.

Summary: 
John's supervisor postponed the meeting again, which made him angry. He wants to change his supervisor, but it's not easy. He will talk to him, maybe he will agree to resign.