The ornamental design for an undergarment, as shown and described.
FIG. 1 is a front elevation view of the undergarment of the present invention;
FIG. 2 is a rear elevation view thereof;
FIG. 3 is a front elevation view of the undergarment of the present invention with the top partially folded down;
FIG. 4 is a front elevation view of the undergarment of the present invention with the top fully folded down;
FIG. 5 is a rear elevation view of the undergarment of the present invention with the top fully folded down;
FIG. 6 is a left side elevation view of the undergarment of the present invention with the top fully folded down; the right side view being a mirror image thereof;
FIG. 7 is a left side elevation view of the undergarment of the present invention with the top pulled up;
FIG. 8 is a right side elevation view of the undergarment of the present invention with the top pulled up;
FIG. 9 is a top plan view thereof; and,
FIG. 10 is a bottom plan view thereof.
The partial human figure in FIGS. 1-8 and the jeans of FIG. 3 shown in broken lines in the drawings illustrate environmental matter and form no part of the claimed design.