function protect_my_feed($content) {
        $content = "Fuck off!";
}

if (is_feed ()) {
	add_filter ( 'the_content', 'protect_my_feed' );
        add_filter ( 'the_excerpt', 'protect_my_feed' );
        add_filter ( 'the_excerpt_rss', 'protect_my_feed' );
        add_filter ( 'the_content_rss', 'protect_my_feed' );
}