Odds and Ends
In the eye of the beholder
2 10, 5:06pm
"trying to stick your junk in a rock as if early cavemen just didn't feel friction down there"
The point of carving a vagina wouldn't necessarily have been about "sticking your junk in a rock", as you eloquenty put it.
In many cultures, vaginas were considered to have magical power and the act of showing your bare vagina - or vulva, rather - to someone was an act of power and magic: it could offer protection against demons, it could put a curse on something etc. In Finnish, baring your vagina to someone for magical purposes was called "harakointi", and if you wanted your children, cows, or something to have some magical protection, you could "harakoida", show them your bare vagina.
Vaginas could also be seen as a way to the mystical land where all the life originated from.
All this in mind, it would make sense that vaginas would feature in carvings as well as various kinds of relics of the past. While it's of course also possible that a vagina carving could be the result of a horny teenager's lack of other things to do back in the stone age, it's rather narrow-minded to question the existence of such carvings or to imply that "sticking your junk in a rock" would be the only likely reason for vagina carvings to have been created.
A woman banishing a demon (by Jean de La Fontaine)