Red Sox fans are envious of Yankee fans because Yankee fans have been spoiled for ever and the Red Sox wish they had that. Boston has always been riding in the back seat and they want the glory so they get annoyed with the Yankees.
Sox fans definitely used to be, but not in the last few years. Red Sox fans honestly don't give a **** about how many world series the yankees have won like 40 years ago. The important thing as that we won more recently than the yankees.
Here's a few reasons why many Red Sox fans hate the yankees and their fans:
1. There are tons of yankee fans who are just bandwagon fans. Bandwagon fans suck.
2. A lot of yankees fans (many of them are the bandwagoners) are fair-weather fans. when something starts going bad, (for example: a-rod in the post season), they start booing and give up.
3. the evil empire. Steinbrenner trys to buy championships by outbidding and paying a ******** of money to make a team full of allstars. (arod a few years ago)
4. Stealing players from the red sox. Clemens, Damon (he sucks anyways), etc.
I could go on even more, but I don't feel like it.
I have nothing against the dedicated yankees fans (except that they are yankees fans

) who have supported their team unconditionally just like many Red Sox fans over those 86 years.