Background Pony #557B

There's an expression that goes "everything but the kitchen sink" and then people include the kitchen sink for laughs. For example Super Smash Bros is said to have "everything but the kitchen sink" so some will include it in fake character selects (this goes back more then 15 years).For Rainbow Dash, she was said to be shipped with "everything but the kitchen sink" so people starting making fanfiction and fanart shipping her with the kitchen sink. Then it picked up from there and became a meme.