The ornamental design for a universalhairdiffuser, as shown and described.
FIG. 1 is a first perspective view of a universal hair diffuser showing my new design;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a back view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top view thereof;
FIG. 8 is a bottom view thereof;
FIG. 9 is a perspective view of another state of the universal hair diffuser thereof; and,
FIG. 10 is an enlarged view of the selected portion in FIG. 2.
The broken lines shown in the drawings depict portions of the universal hair diffuser in which the design is embodied that form no part of the claimed design.