The ornamental design for a coffeegrinder, as shown and described.
FIG. 1 is a perspective view of a coffee grinder showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a back elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is bottom view thereof.
The evenly dashed broken lines illustrate parts of the coffee grinder that form no part of the claimed design. The dot-dashed broken lines show the bounds of the claim and form no part of the claimed design.