The ornamental design for an electrictoothbrush, as shown and described.
FIG. 1 is a front, right side and top perspective view of an electric toothbrush showing my design.
FIG. 2 is a rear, left side and bottom perspective view thereof.
FIG. 3 is a front elevation view thereof.
FIG. 4 is a rear elevation view thereof.
FIG. 5 is a left side elevation view thereof.
FIG. 6 is a right side elevation view thereof.
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken lines shown in the drawings are included for the purpose of illustrating portions of the electric toothbrush that form no part of the claimed design.