dieting panties
Panties which are smaller than the intended wearer's current size and intended to serve as motivation for her diet (course of action to reduce body weight, size, or fat) or to serve as a marker of when her diet has achieved its intended goal.
The aspiring ballerina purchased a pair of size double-zero lace panties with a 20-inch waist and said to herself, "I will not eat solid food until I fit into these dieting panties. And even then, I will diet to remain slim enough to fit in them." She eagerly anticipated the feeling of the delicate lace against her glabrous vulva, and her hunger temporarily subsided.