The ornamental design for a coffeemug, as shown and described.
FIG. 1 is a top front isometric view of a coffee mug showing my new design;
FIG. 2 is a bottom rear isometric view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a left side elevation view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The features shown in broken lines in the drawing depict portions of the design that form no part of the claimed design. The dash-dot-dash lines in the drawings represent the bounds of the claim and form no part of the claimed design.