Business on top, party town down below. Yes, the mullet of the suiting industry — deemed “the shortie” — is back and bigger than ever. But will the tricky trend go mainstream? That’s what insiders are forecasting as retailers from Barneys to J.Crew line up to get a ticket on this party bus. From monochromatic iterations at ICB and Adam Lippes to the pattern play at Tory Burch and GANT Rugger, nine to five has never looked so good.