The ornamental design for a butterstickslicer, as shown and described.
FIG. 1 is a perspective view of a butter stick slicer showing my new design, the scale and legend signs are shown in broken lines for illustrative purposes only and form no part of the claimed design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a side view thereof, the opposite side being a mirror image;
FIG. 4 is a bottom plan view thereof; and,
FIG. 5 is an end view thereof, the opposite end being a mirror image.