WP Admin Bar frontend issue with dashicon deregister

Well, the dashicons are used in the admin bar, so if you deregister them, your admin bar is broken. The easy way out is only to deregister the icons if there is no admin bar:

add_action( 'wp_print_styles', function() {
    if (!is_admin_bar_showing()) wp_deregister_style( 'dashicons' );
}, 100);