The ornamental design for men's boxer underwear, as shown and described.
FIG. 1 is a front elevation view of the men's boxer underwear of the present design; shown in a state whereby the fastener strips are engaged;
FIG. 2 is an interior plan view of the men's boxer underwear of FIG. 1 laid flat.
FIG. 3 is an exterior plan view of the men's boxer underwear of FIG. 1 laid flat;
FIG. 4 is a side elevation view of the men's boxer underwear of FIGS. 1-3 in use, shown in a state whereby the fastener strips are engaged; the broken lines showing a partial human figure are for purposes of illustrating environment and form no part of the claimed design;
FIG. 5 is a side elevation view of the of the men's boxer underwear of FIGS. 1-4 in use, illustrating the hook and loops portion of the men's boxer underwear in an unconnected state; the broken lines showing a partial human figure are for purposes of illustrating environment and form no part of the claimed design; and,
FIG. 6 is an enlarged view of the tab section located on the men's boxer underwear of FIGS. 1-4; the broken lines are boundaries of the detail and form no part of the claimed design.