I claim the ornamental design for a Yin Yang mug, as shown and described.
FIG. 1 is a perspective view of a Yin Yang mug showing my new design;
FIG. 2 is a left side elevational view thereof;
FIG. 3 is a right side elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a front elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design. Any surfaces not shown, including interior surfaces, form no part of the claimed design.