It is a melding of the 2 words, nasty and fashion. Coined in a sewing lab many years ago, to describe totally ghetto rigging a garment together to make it look good, not using any actual technique or skill. It has evolved to mean throwing anything together to make it look nice, fashion or non fashion.
That sleeve is WAY too big to be sewn into that armhole, but I nashioned it together.
I am so good at making shit work, I should be called a Nashionista.
I would totally buy that shirt,but I know that designer just nashions everything.