The ornamental design for a bambooguitar, as shown and described.
FIG. 1 is a front and side perspective view of a bamboo guitar showing my new invention;
FIG. 2 is a front elevational view thereof, shown at an enlarged scale and with only a portion of the unclaimed environment shown for ease of illustration;
FIG. 3 is side elevational view thereof; and
FIG. 4 is a back elevational view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 bottom plan view thereof.
The broken lines shown in the drawings are for illustrative purposes only and form no part of the claimed design.