The ornamental design for boxer shorts, as shown and described.
FIG. 1 is a perspective view of boxer shorts illustrating my new design;
FIG. 2 is a front plan view of FIG. 1 which also illustrates, in broken lines, a logo-tag;
FIG. 3 is a rear plan view of FIG. 1;
FIG. 4 is a right-side view of FIG. 1;
FIG. 5 is a left-side view of FIG. 1;
FIG. 6 is a top-end view of FIG. 1; and,
FIG. 7 is a bottom-end view of FIG. 1.
The broken lines shown in the Figures of the logo-tag, seams and stitching, as well as their size and configuration, illustrate the environment only and form no part of the claimed design.