The ornamental design for a park bench entertainment device, as shown and described.
FIG. 1 is a perspective view of a park bench entertainment device showing my new design, the broken line showing of a park bench illustrates environment only and forms no part of the claimed designed;
FIG. 2 is an enlarged front view of a park bench entertainment device; and,
FIG. 3 is a right side view of a park bench entertainment device, the left side being a mirror image thereof.