The ornamental design of a bottle opener, as shown and described.
FIG. 1 is a perspective view of a bottle opener showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a side elevation view, the opposite side view is a mirror image thereof; and,
FIG. 4 is a bottom plan view thereof.
The broken lines are provided for illustrative purposes only and form no part of the claimed design. In addition, the portions of the bottle opener that are not shown in the drawing do not form any part of the claimed design.