Fluttershy knows the sort of music she likes, and also knows that it definitely isn't the sort of music that Rainbow Dash likes. Still, friends make sacrifices for one another, so when Rainbow Dash brings her to a Nine Inch Hooves show, Fluttershy does her best to fit in.
Very mild Season 8 Episode 4 spoilers, although watching the episode first might help this story make more sense.
Written while heavily under the influence of Nine Inch Nails.