The ornamental design for a hairbrush, as shown and described.
FIG. 1 is a front right perspective view of a hairbrush showing my new design;
FIG. 2 is a rear perspective view of the hairbrush shown in FIG. 1 with a pop socket in a closed position;
FIG. 3 is a rear perspective view of the hairbrush shown in FIG. 1 with a pop socket in an open position;
FIG. 4 is a front elevation view of the hairbrush shown in FIG. 1;
FIG. 5 is a rear elevation view of the hairbrush shown in FIG. 1;
FIG. 6 is a left side elevation view of the hairbrush shown in FIG. 1;
FIG. 7 is a right side elevation view of the hairbrush shown in FIG. 1;
FIG. 8 is a top plan view of the hairbrush shown in FIG. 1; and,
FIG. 9 is a bottom plan view of the hairbrush shown in FIG. 1.
The broken lines in FIGS. 1-9 illustrate portions of the hairbrush that from no part of the claimed design. The dash-dot-dash broken lines in FIGS. 1-7 illustrate the boundary of the claimed design which forms no part thereof.