Sounds like your son is in for a wild party lol!
I would probably just ask the local cake place to help out, as they probably have experience with this kind of thing, especially for bachelorette parties and stuff...
If you're going for it yourself, then the key is just getting the fondant icing right: The right texture and color. Then work on shaping the outer labia, more than anything else, that part is crucial.
Then you can go back in for the details, and you might want to add some icing or sprinkles for the pubes etc...
The best thing if you are doing this at home is to find and follow along with a video as they break it up into steps...
some of them are pretty weird, but i have found a few (can't BELIEVE I have between watching so many vagina cake making vids today)
