This is how my hermaphrodite slugs do it:

For better and more bizarre slug action, check out Home of Slug Love where you can see banana slugs getting it on… and getting it bitten off!

When they mate, they insert their penises into eachother at the same time. The unusual thing (in case you don’t find that unusual enough!) is that sometimes, but not always, when they finish mating one slug will chew the penis completely off the other, a process called Apophallation. Sometimes it happens that both slugs engage in chewing so that at the end of the mating encounter, both slugs are penis-less.