Cats may bite, and geese may have barbed penises, but one newly described hermaphroditic sea slug has taken violent animal sex to a new level by stabbing its mates in the head.

The perpetrator of this bizarre act, Siphotperon sp. 1, is a small sea slug found off the northeast coast of Australia. A simultaneous hermaphrodite, it has both male and female reproductive organs that it uses simultaneously during sex.

For its male organ, the slug has a two-pronged penis consisting of a penile bulb that transfers sperm, and a separate, needlelike appendage called a penile stylet that stabs and injects partners with prostate fluid-containing sex hormones called allohormones.
...
But Siphotperon sp. 1 was the only of its relatives that consistently stabbed its partner between the eyes. This is the first known instance of such reproductive head-butting in the animal world, the team reports today (Nov. 12) in the Proceedings of the Royal Society B.



Here.

I saw this in a couple of places, but I haven't seen anything about whether they had a second date...