Susanne Bartsch frowned into a ceiling-high mirror, lifting her left breast with her palm. “This one looks droopy,” she said, in her Swiss-German accent. She turned and examined her svelte profile, adding proudly, “They’re only a year old.”

It was nearing 11 p.m. on a Thursday, and Ms. Bartsch, flanked by a pair of stylists and her yapping schnauzer, Bippy, had been primping in her boho-chic Chelsea Hotel apartment for more than an hour. Not that the process is ever brief; for Ms. Bartsch, the Swiss Miss of New York night life since the Koch era, dressing up is as meticulous an art form as decoupage.

But on this particular night, still jet-lagged from a jaunt to Singapore, Ms. Bartsch was exasperated. Her makeup was all wrong. (“I wanted rhinestone dots, not black splatches!”) A ruffled harness with a giant pink bow, which slung up around her shoulder from her petite waist, had no identifiable front or back. Same with an enormous, custom black wig, which was shaped like a sousaphone ...