Why does everybody hate The Mysterious Mare Do Well?

What I dislike about the episode is the fact that the 5 are humiliating Rainbow Dash at all. This is out of character behavior of worst kind. This isn't a friendship, but some kind of toxic relationship. As far as we know she wasn't harming anybody, so the 5 was suppressing RD for acting outside of social standard. Imagine bulling FS for being shy and spending lots of time with animals, or TS for reading too many books, etc.