I claim the ornamental design for the headphone pillow, as shown and described.
FIG. 1 is a rear perspective view of the headphone pillow in use;
FIG. 2 is a front perspective view of the headphone pillow in use;
FIG. 3 is a rear perspective view of the headphone pillow;
FIG. 4 is a top view of the headphone pillow;
FIG. 5 is a right-side view of the headphone pillow;
FIG. 6 is a bottom view of the headphone pillow; and
FIG. 7 is a left-side view of the headphone pillow;
FIG. 8 is a rear view of the headphone pillow; and,
FIG. 9 is a front view of the headphone pillow.
The broken line illustration of environmental structure in the drawing is not part of the design sought to be patented. As such, the over the ear stereo headphones are shown in broken lines for illustrative purposes only and forms no part of the claimed design.