The ornamental design for a double opening boxer shorts, as shown and described.
FIG. 1 is a front elevational view of double opening boxer shorts, showing my new design, shown in use;
FIG. 2 is a right side elevational view thereof;
FIG. 3 is a left side elevational view thereof;
FIG. 4 is a back elevational view thereof, shown in use;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a front elevational view thereof; and,
FIG. 8 is a rear elevational view thereof.
The broken lines depicting the human form in FIGS. 1, 4, and on the lower right portion in FIGS. 1 and 7 are for environmental structure only and form no part of the claimed design.