The ornamental design for a toothbrushstand, as shown and described.
FIG. 1 is a front/right/top perspective view of a toothbrush stand;
FIG. 2 is a rear/left /bottom perspective view thereof;
FIG. 3 is a front elevational view thereof (a rear elevational view would be a mirror image thereof);
FIG. 4 is a right side elevational view thereof (a left side elevational view would be a mirror image thereof);
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The outer broken-line circle in FIGS. 2 and 6 represents the bounds of the claimed design, while all other broken lines are directed to environment; the broken lines in the Figures are for illustrative, environmental purposes only and form no part of the claimed design.