During the act of doggie style sex the male pulls back to far and pops it into the rear door without notice. It is a mix of combining a surprise penetration for both parties.
He was reaming her from behind when he pulled back to far and they became penetrised by the illegal entry .
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi