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 design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof; and,
FIG. 5 is another perspective view with a capped bottle and optional handle shown in broken lines.
The dash-dot-dash and dot-dot-dot broken lines are included for the purpose of illustrating environmental elements that form no part of the claimed design.