FIG. 1 is a perspective view of a toothbrush cover showing my new design; FIG. 2 is a front elevational view of FIG. 1; FIG. 3 is a rear elevational view of FIG. 1; FIG. 4 is a side elevational view taken from the left of FIG. 3; FIG. 5 is a top plan view of FIG. 1; and, FIG. 6 is a bottom plan view of FIG. 1.