What the hay is this?
"Rainbow Dash Always Dresses In Style" is an image macro that is frequently used to troll other Ponychan users. A large majority of bronies are fans of only the current "G4" ponies and Friendship is Magic. The aforementioned image macro is taken from a screenshot of the title sequence from the G3.5 My Little Pony series, and the caption is taken from a line in the theme song. Older generations are perceived (often correctly so) as far more girly than the current series, and are seen as bastardized or corrupted as such. The reason that this particular macro is so effective is because it is the polar opposite of the G4 Rainbow Dash. While G3 Rainbow Dash is far more stereotypically girly, dealing with fashion and shopping, G4 Rainbow Dash is very tomboyish and athletic
The picture itself is usually posted with a spoiler, giving it a "bait-and-switch" style usage, but when it is not, most people react with mock horror and demand that it be spoilered or deleted. It is also frequently met with responses such as "Jesus Christ, how horrifying" or "Kill it with fire"
(most ponies anyway)