Did you enjoy the movie Sideways? Sure you did. Most people did. In Japan though it wasn't as big of a hit, so some Japanese producers decided to do their own version. Instead of focusing just on wineries around Santa Barbara they decided to also include Napa and other wine regions in California. The remake was a big hit in Japan and also increased California wine sales in Japan.
The producers decided to offer Paul Giamatti a cameo in the movie, but he declined, saying, "I said no. I felt my career hasn't hit that low yet. I thought, 'What am I gonna play - the sushi chef or something?'" That is a really nice attitude to take. It is just a cameo. Actors do cameos all the time as favors and I think it would have been kind of cool to see him in it and probably would have made people watch the original Sideways again and possibly generated additional revenue for Giamatti. Maybe he could have done some commercials in Japan also and made some money. Accepting a cameo isn't going to hurt your career even in the worst movie of all time. It is a cameo, and nothing more.
Paul didn't just leave it at that though, he decided to trash the actor who played him in the remake. "They got a strange, little troll to play me." The strange troll, Giamatti is referring to is Fumiyo Kohinata. I don't know what mirror Paul uses every morning, but he isn't exactly the best looking guy to ever walk the earth. I also think that he has probably ruined any chance of any of his movies doing any kind of business in Japan. In the US we always remake Japanese movies, and I don't think I have ever heard of one of their original actors calling any of the actors in a remake a derogatory term.