The ornamental design for a teethingdevice, as shown and described.
FIG. 1 is a perspective view of a teething device showing our new design;
FIG. 2 is a perspective view of the teething device of FIG. 1;
FIG. 3 is front elevational view of the teething device of FIG. 1;
FIG. 4 is a rear elevational view of the teething device of FIG. 1;
FIG. 5 is a right side elevational view of the teething device of FIG. 1, the left side elevational view being a mirror image of the right side elevational view; and,
FIG. 6 is a top plan view of the teething device of FIG. 1, the bottom plan view being a mirror image of the top plan view.
The broken lines illustrate portions of the teething device which form no part of the claimed design.