BuddyPress.org

It works like this:

add_filter('bp_get_activity_show_filters_options', 'my_buddypress_filter',10,2);
function mp_buddypress_filter($filters, $context) {
  $filters['new_blog_post'] = 'Blog Posts';
  $filters['new_blog_comment'] = 'Blog Comments';
  $filters['bbp_topic_create'] = 'Forum Topics';
  $filters['bbp_reply_create'] = 'Forum Replies';
  return $filters;
}