hard shell
If you have a high bone density, then you have a hard shell- meaning a skeleton that is tough to break or fracture.
Larry fell out of tree and broke no bones, he must have a hard shell!”
Hard Shelling
the act of female teabagging.
Rick: dude Jenny is totally going around hard shelling everyone
Hard Shell Taco
The equivalent of "Morning Wood" Hard Shell refers to the hardened clit and Taco refers to the vagina.
"I woke up with a major Hard Shell Taco today."