I claim the ornamental design for a personal vaporizer, as shown and described.
FIG. 1 is an exploded perspective view of a personal vaporizer showing my new design with the cap portion separated from the base for clarity of disclosure;
FIG. 2 is a side elevational view of the base portion of the personal vaporizer:
FIG. 3 is a top plan view of the base portion of the personal vaporizer; and,
FIG. 4 is a bottom plan view of the personal vaporizer.