The ornamental design for a hardhat, as shown and described.
FIG. 1 is a frontal perspective view of a hardhat showing my new design with a ventilation strip thereof shown in a closed attitude;
FIG. 2 is a rear perspective view thereof with the ventilation strip shown in an open attitude;
FIG. 3 is a front elevational view thereof with the ventilation strip shown in the closed attitude;
FIG. 4 is a rear elevational view thereof with the ventilation strip shown in the closed attitude;
FIG. 5 is a right side elevational view thereof with the ventilation strip shown in the closed attitude, the left side elevational view being a mirror image thereof;