In GF III Johnny Fontaine comes from Vegas to perform at Michael's party and as soon as he starts to sing Michael gets up to leave the room despite Johnny's pleas to stay to listen to his favorite song. Michael makes fun of the title ("For Each His Own") saying something like "Salsice His Own" and then says he is going to go listen to his favorite Tony Bennett records. Is this Michael's idea of a joke or is there some bad blood no one seems to know about?

What I don't know is why anyone would like Johnny.

He was just someone they used to bring people into the Casinos. I doubt Vito's fondness for Johnny transferred to his sons.

Most likely that's true.
Also, I think that scene was a kind of heavy-handed attempt to give Michael a "sense of humor"

Connie and Mary seemed to like him. If that was an attempt to show Michael had a sense of humor, then it may rate near the top, or bottom if you will, of bad writing in GFIII.

Gota love that scene tho

I read two things into that exchange:

1. Michael is hurrying off to see Kay. It's our first clue of how much he misses her.

2. I thought the dialogue wasn't an attempt to show humor, but to show what a politician Michael has become. His meaningless, good-natured banter reminds me of Geary.

Another sign that Michael wants to get rid of his past. In part 3 he is totally out of the mafia thinking. He needs lawyers,not tough guys!

If anything in this life is certain, if history has taught us anything, it's that not even a lawyer can stop Johnny Fontane and his guinea charme and his olive oil voice.

It could have been a somewhat "inside" joke, as we all know that the character Johnny Fontaine was based on Frank Sinatra, and Frank Sinatra's favorite singer was Tony Benett