My brother has decided that he wants his s p a c e o u t nickname to be Hard Core Jelly.
That was my pick for him too. He plays the drums and and can play for over half an hour straight and to be able to do that it requires a strong stomach i.e a hard core. So in that case he has a hard core. But when he's not banging on the drums his core is so soft it feels (and even wobbles) like jelly.

Hence the name Hard Core Jelly