I heard such a phrase being used from Youtube, often from thrifters which is one of my favorite pastimes. At times I see a piece which is costumey but if styled differently can be normalized. For instance, Halloween costumes… I know it sounds like a far stretch specially when it comes to the raunchy outfits or over the top props, but I’m more leaning towards the themed pant suits and quirky nylons. As long as it meets ones comfort level then I say why not? I wore a wig one time for a casual night out to my favorite bar and the bartender didn’t recognise me. Unfortunately due to the humidity out here I seldom wear a wig nowadays since it gets too hot.
Bottom line is, its on the eye of the beholder. One piece or an outfit might be costumey for one but it might not be for another. Therefore, one’s norm isn’t exactly the same as the next person. Also, what we consider weird might be someone else’s normal.
In the end, its not the matter of being costumey its more of pushing the boundary of what’s considered “normal.”