The ornamental design for a computermouseskin, as shown and described.
FIG. 1 is a front isometric view of a computer mouse skin in accordance with the new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof; and,
FIG. 6 is a top plan view thereof.
The broken lines shown in FIGS. 1-6 are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.