The ornamental design for toothbrush, as shown and described.
FIG. 1 is a top plan view of toothbrush embodying my new design;
FIG. 2 is a left side elevational view thereof, the right side being a
mirror image of the side shown; and,
FIG. 3 is a bottom plan view thereof.
The portions of the front and rear end surfaces of the article neither
shown in the drawing nor described in the specification form no part of
the claimed design.