The ornamental design for a pivot plunger, as shown and described.
FIG. 1 is a perspective view of a pivot plunger showing the new design.
FIG. 2 is a top view of the pivot plunger of FIG. 1.
FIG. 3 is a bottom view of the pivot plunger of FIG. 1.
FIG. 4 is a first side view of the pivot plunger of FIG. 1.
FIG. 5 is a second view of the pivot plunger of FIG. 1.
FIG. 6 is a third side view of the pivot plunger of FIG. 1; and,
FIG. 7 is a fourth side view of the pivot plunger of FIG. 1.
The broken line showing of portions of a pivot plunger is included for the purpose of illustrating environmental structure and forms no part of the claimed design.