Flatworms

Having both male and female reproductive organs (hermaphrodites), the flatworms really do have to fight for their right to party. The life of a male is far more desirable as it is much easier than that of the females, as any female reading this will attest to.

After the mating is finished, the male can just swim off to go and hang out at his local watering hole with his buddies, leaving the female to raise the kids. Due to the fact the female has to dedicate time and resources to their young, if either of them wants the male role, they’ve got to fight for it.

Being males, of course they challenge each other to a duel…..with their penises. Whoever manages to stab the other first then earns the right to be the lazy dead beat dad.