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!”
by Urbandefinitionsaremypassion December 12, 2017
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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."
by something_else February 21, 2015
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