in the altogether
Also, in or stripped to the buff; in the raw. Naked, nude, as in The art class wanted a model to pose in the altogether, or She was stripped to the buff when the doorbell rang, or He always sleeps in the raw. The first of these colloquial terms dates from the late 1800s. In the buff, a seemingly modern locution dates from the 1600s, buff alluding to a soft, undyed leather, buffskin, that also gave its name to the color. The use of raw, presumably also alluding to raw (undressed) leather, dates from the early 1900s.