The ornamental design for as back vest, as shown and described.
FIG. 1 is a rear perspective view of a back vest of conventional thickness
showing my new design in use, the broken lines partially showing a human
form being for illustrative purposes only and forming no part of the
claimed design, and the broken lines on the claimed vest throughout the
views are understood to represent conventional stitching;
FIG. 2 is a front elevational view thereof; and,
FIG. 3 is a rear elevational view thereof.
The rectangular tabs on the upper straps are understood to represent
conventional hook and loop closures.