I hate anything NY...doesn't even matter if they have the nicest fans ever. It stems from growing up in NE and intensely disliking everything about NYC whenever I visited (which was at least once a year since I have an aunt and uncle from there). It's a bonus that they end up being even more unlikable because of the obnoxious fans, but honestly, every city and every team has fans like that (I went to Seattle, and met some really dick fans there that said I was a bandwagon Patriots fan...yeah, like I'm not about 30 minutes from Gilette and have cheered for really shitty Patriots teams most of my life).
I don't REALLY hate the Mets, as I only started to follow baseball and the Red Sox in the early 90s, so I don't have 1986 to think about. However, being a Sox fan, you kind of have to hate the Mets, even if they have been shitty for such a long time. That being said, they are way, way, way, way, way behind the hatred for the Yankees.