The ornamental design for a beardstraighteningbrush, as shown and described.
FIG. 1 is a top, rear and right-side perspective view of a beard straightening brush showing my new design;
FIG. 2 is a bottom, front and left-side perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof; and,
FIG. 9 is an enlarged view of portion 9 shown in FIG. 2.
The evenly-incremented broken lines in the drawings depict environmental structure, while long-dash-short-dash broken lines illustrate the bounds of the enlarged detail view. None of the elements depicted in broken lines form part of the claimed design.