The ornamental design for a toothpick, as shown and described.
FIG. 1 is a perspective view of a toothpick showing my new design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a side view thereof;
FIG. 5 is an opposite side view thereof;
FIG. 6 is rear view thereof; and,
FIG. 7 is a front view thereof.
The broken lines shown in FIGS. 1-7 illustrate portions of the toothpick that form no part of the claimed design. The broken lines within the circular elements illustrate portions of the toothpick that form no part of the claimed design. Additionally, the area between the claimed circular holes and the broken lines forms no part of the claimed design.