The ornamental design for a horseheadhat, as shown and described.
FIG. 1 is a front perspective view of the horse head hat showing my new
design;
FIG. 2 is a rear perspective view of the horse head hat and illustrating my
new design;
FIG. 3 is a bottom perspective view of the horse head hat of my new design;
and,
FIG. 4 is a side perspective view of the horse head hat, the broken line
showing of the human form is for illustrative purposes only and forms no
part of the claimed design.