The ornamental design for a mugdecoration, as shown and described.
FIG. 1 is a right side view of a mug decoration of the present invention;
FIG. 2 is a front view of the mug decoration of FIG. 1; and,
FIG. 3 is a rear view of the mug decoration of FIG. 1.
The broken line showing of a mug in FIGS. 1-3 is for illustrative purposes
only and forms no part of the claimed design. The left side view is a
mirror image of the right side.