The ornamental design for a guitar pick holder comprising a flexible magnetic body, as shown and described.
FIG. 1 is a front elevational view of a guitar pick holder made of a flexible magnetic body, showing front surface of the guitar pick holder for magnetically attracting and holding magnetically attractable guita picks showing my new design;
FIG. 2 is a top plan view thereof, the bottom being identical;
FIG. 3 is a rear elevational view of FIG. 1, showing a rear surface of the guitar pick holder for adhering to a guitar surface or the like; and,
FIG. 4 is a left elevational view thereof, the right side being identical.