crown jewels

noun[plural only]2

1. •
   The jewelry that accompany the office of rulership in a monarchy, i.e. crown, scepter, signet ring, etc.

   • The crown jewels in the United Kingdom are heavily guarded and anyone trying to steal them will certainly have a hard time.
2. •
   (slang, euphemistic) The male genitalia.

   • The whole crowd cringed as he got kicked in his crown jewels.