I claim the ornamental design for 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 top plan view thereof;
FIG. 3 is a right-side elevational view thereof;
FIG. 4 is a front elevational view thereof, the rear elevational view being a mirror image thereof;
FIG. 5 is a left-side elevational view thereof; and,
FIG. 6 is a bottom plan view thereof.
The broken lines showing a person's hand opening a bottle in FIG. 1 and a magnet in FIG. 6 depict environmental matter and form no part of the claimed design.