The ornamental design for a hairiron, as shown and described.
FIG. 1 is a perspective view of a hair iron showing the design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken line showing of the interior of the hair iron and electrical connections are included for the purpose of illustrating portions of the article and form no part of the claimed design.