How to remove the Admin Bar in WordPress 3.1 correctly

Although the WordPress Admin Bar can be hidden by a user visiting their profile page in the Admin Panel (Users > Your Profile), there may be a situation where you want to force the removal without instructing the user to amend their settings or updating their settings automatically.

When the issue of removing the Admin Bar first cropped up, the solution was to remove the associated init action, however this is not the correct method of disabling it and should not be used.

remove_action('init', 'wp_admin_bar_init');

Instead, you either use the show_admin_bar filter and simply return false:

function hide_admin_bar() {
    return false;
}
add_filter( 'show_admin_bar', 'hide_admin_bar' );

Or alternatively call the show_admin_bar function directly:

show_admin_bar( false );

If you are disabling the bar from within an init action it is important that you correctly pass the priority value, otherwise some of the assets may remain (such as the JavaScript file) and cause unwanted behaviour.

Using a priority of 9 seemed to be be the most successful from my experiments, although other possibilities may be used:

add_action( 'init', 'my_init_function', 9 );

There are a number of comments in the source code of 3.1, discouraging you from using the previous method of removing the wp_admin_bar_init action, so encourage anyone to update the method they are using.

All of the methods mentioned here can be used in either your plugin file or functions.php file.