I'm buying more and more into the idea that Bad Blood was meant to be a send-up of Katy's lyrics like she dragged Mr. Mayer by aping his style in Dear John. It'd be kind brilliant, if true.
Somehow the "what was shiny, now it's all rusted" line comes across as exactly the kind of "went for universal, wound up clunky" attempt at metaphor ("...like a plastic bag") that

Katy

would come up with.
Either way they seem kinda uncharacteristic for Taylor. For all the criticisms that have been made against her lyrics (that they're too childish/broad; overly saccharine), she has never been one to not know her way around a turn of phrase.