bbp_is_custom_post_type( mixed $the_post = false )

function bbp_is_custom_post_type( $the_post = false ) {

	// Assume false
	$retval = false;

	// Viewing one of the Forums post types
	if ( in_array( get_post_type( $the_post ), array(
		bbp_get_forum_post_type(),
		bbp_get_topic_post_type(),
		bbp_get_reply_post_type()
	) ) )
		$retval = true;

	return (bool) apply_filters( 'bbp_is_custom_post_type', $retval, $the_post );
}