Another reason why United fans hate Chelsea is because they didn't like it when they had direct competitors for titles. And also because Chelsea sack managers at the first sign of trouble. And Manchester United fans were very proud of the fact that they liked to hire long term managers. read more
So that’s another reason why Chelsea fans get a lot of stick. Other clubs who had a reputation for hooliganism at the time were Millwall, West Ham and Leeds United. That’s another origin of the Chelsea hate. read more
Chelsea is obviously extremely hated within England and especially by the other big PL teams such as Liverpool, Arsenal, Manchester United, etc. Additonally, Chelsea has had heated games and results against Barcelona and Bayern Munich, so fans of those two clubs aren't exactly in love with Chelsea. read more