Some flatworms, for instance these pretty Pseudobiceros hancockanus, engage in penis fencing. Both individuals are hermaphrodites, i.e., have both male and female organs. The penis is white, pointed and two-headed. Both individuals are trying to inseminate the other. The one who is inseminated has to bear and lay eggs - a more expensive proposition. The one who "won" the fencing bout and did the insemination can move on and fence some other guys and on and on, "fathering" many progeny until happenning onto a better fencer, getting inseminated, and spending the rest of the life as "mother".